UNIVERSITY  OF  CALIFORNIA 


OIKT 


Received 
Accession  No  . 


No  . 


11V 


vy 


3| 

Z^/    S 


kr  <v 


THE 


ELEMENTS  OF  CHEMISTRY 


BY 

PAUL  C.  FREEB,  M.D.,  PH.D.  (MUNICH) 

UNIVERSITY  OF  MICHIGAN 


Boston 

ALLYN    AND    BACON 

1895 


COPYRIGHT,  1895, 
r  PAUL  C.  FREER. 


PETEBS  &  SON 
BOSTON. 


PREFACE. 


IN  undertaking  an  ELEMENTARY  CHEMISTRY,  I  was 
actuated  by  a  growing  conviction  that  the  methods  of 
teaching  beginners  now  very  generally  in  vogue  do 
not  make  prominent  what  is  essential  in  the  science. 
In  the  following  pages  I  have  endeavored  thoroughly  to 
familiarize  the  pupil  with  the  general  aspects  of  chemi- 
cal changes,  using  only  a  few  of  the  most  important 
elements  and  compounds  for  the  purposes  of  illustra- 
tion ;  the  work  is  quantitative,  both  in  the  text  and 
laboratory  appendix.  Chemistry  is  growing  to  be  more 
of  an  exact  science  every  day,  and  in  it  quantitative 
work  can  no  more  be  neglected  than  it  can  in  the  study 
of  physics.  The  atomic  theory  is  not  introduced  until 
the  pupil  has  sufficient  chemical  experience  to  compre- 
hend its  meaning  and  advantages,  and  until  he  thor- 
oughly understands  that  theories  are  based  on  facts,  not 
facts  on  theories.  The  theory  of  valence  I  have  only 
briefly  touched  upon,  as  it  is  not  necessary  for  an  under- 
standing of  Elementary  Chemistry.  Its  dogmatic  appli- 
cation may  be  productive  of  more  harm  than  good. 

Chemical  Equations  I  have  avoided  as  much  as  possi- 
ble, because  I  wished  to  give  them  only  the  relative 
importance  which  belongs  to  them.  The  too  frequent 
use  of  these  equations  may  lead  to  the  view  that  all 

iii 


iv  ELEMENTS   OF  CHEMISTRY. 

reactions  which  can  be  so  formulated  must  in  reality 
take  place. 

The  domain  of  so-called  physical  chemistry  is  con- 
stantly growing,  and  can  no  longer  be  ignored  in  works 
of  this  kind.  •  For  this  reason  I  have  introduced  some 
of  the  simple  general  facts  which  have  been  universally 
adopted  in  this  branch  of  the  science,  notably  under  the 
head  of  electrolysis  and  double  decomposition. 

The  laboratory  experiments  are  largely  quantitative  in 
their  nature.  Experience  has  shown  me  that  none  of 
them  are  too  difficult  for  beginners.  It  has  been  too 
much  the  custom  to  seek  easy  experiments,  without 
considering  whether  such  experiments  would  teach 
general  principles  and,  above  all,  would  emphasize 
quantitative  relations.  In  the  study  of  an  exact  science, 
the  latter  are,  however,  the  most  important. 

I  have  endeavored  to  simplify  the  apparatus  as  much 
as  possible,  and  am  sure  that  the  outfit  required  suc- 
cessfully to  follow  this  book  will  not  be  too  expensive. 
Certain  kinds  of  good  apparatus  every  chemical  labora- 
tory must  have  in  order  to  do  successful  work;  and  in 
all  cases  where  cheap  and  inefficient  things  are  used, 
the  result  is  a  sacrifice  of  science  in  the  interests  of 
economy.  A  good  balance,  a  barometer,  two  gasom- 
eters for  the  storing  of  larger  quantities  of  gases, 
and  a  combustion  furnace  are  the  most  expensive  pieces 
required.  Whatever  is  used  should  be  of  the  best 
quality,  for  exact  results  can  only  be  obtained  by  exact 
methods.  A  chemical  experiment,  when  correctly  per- 
formed, is  as  certain  to  have  an  unvarying  result  as  is 
one  in  physics. 

The  figures  in  the  Appendix  have  all  been  made  from 


PREFACE.  V 

photographs  which  were  taken  from  apparatus  in  actual 
use,  so  that,  if  they  are  used  as  models,  no  difficulty 
will  be  found  in  the  laboratory  work. 

I  wish  to  take  this  opportunity  of  thanking  Mr.  Geo. 
O.  Higley  for  his  assistance  in  compiling  the  laboratory 
appendix,  and  Mr.  Geo.  A.  Bacon  for  his  careful  read- 
ing of  the  manuscript  copy. 

PAUL  C.  FREER. 
ANN  ARBOR,  September,  1895. 


TABLE  OF  CONTENTS. 


PAGE 

CHAPTER  I.     Changes  in  Matter 1-8 

Aims  of  Modern  Chemistry.  —  Phlogiston  Theory.  —  Lavoisier's  Experi- 
ments.—  Law  of  the  Conservation  of  Matter.  —  Importance  of  Correct 
Observation. 

CHAPTER  II.     Chemical  Nomenclature 9-12 

Chemical  Elements.  —  Chemical  Compounds. 


III.     Water 13-18 

Physical  Properties  of  Water.  —  Solutions.  —  Water  of  Crystallization.  — 
Efflorescence  and  Deliquescence.  —  Anhydrous  and  Hydrated  Crystals.  — 
Impurities  in  Water.  — Distillation. 

HAPTER  IV.     Water  (Continued) 19-28 

Action  of  Sodium  and  Potassium  on  Water.  —  Decomposition  of  Water 
by  the  Electric  Current.  —  Formation  of  Water  from  Hydrogen  and  Oxygen. 
—  Relation  of  Hydrogen  to  Oxygen  by  Weight.  —  Summary. 

CHAPTER  V.    Products  of  the  Action  of  Sodium  and 

Potassium  on  Water 29-31 

Caustic  Soda  and  Caustic  Potash. 

CHAPTER  VI.  Changes  of  Energy  -which  take  place  in 
the  Formation  of  Water,  Potassium  Hydroxide,  and 
Potassium  Oxide 32-37 

Energy.  —  Conservation  of  Energy.  —  Changes  of  Energy  in  the  Forma- 
tion of  other  Compounds.  —  Kindling  Temperature. 

CHAPTER  VII.      Hydrogen   Chloride,  Preparation  and 

Properties 33-44 

Decomposition  by  Sodium;  by  the  Electric  Current.  —  Difference  be- 
tween the  Structure  of  Hydrogen  Chloride  and  Water.  —  Formation  of 
Hydrogen  Chloride  from  its  Constituent  Elements. —  Summary.  — Resem- 
blances between  Hydrogen  Chloride  and  Water. 

vii 


Vlil  CONTENTS. 

PAGE 

CHAPTER  VIII.  The  Action  of  Metals  on  Hydrochloric 
Acid.  The  Neutralization  of  Hydrochloric  Acid  by 
Bases 45-52 

Changes  of  Energy.  -.Action  of  Hydrochloric  Acid  on  the  Oxides  and 
Hydroxides  of  the  Metals.  —  Neutralization  of  Hydrochloric  Acid  by  Bases. 
—  Changes  of  Energy.  —  Summary. 

CHAPTER  IX.     The  Oxides  of  Sulphur 53-65 

Acids  and  Salts  in  General.  —  Formation  of  Sulphur  Dioxide  and  Tri- 
oxide.  —  Laws  of  Definite  and  Multiple  Proportions.  —  Formation  of  Sul- 
phuric Acid.  —The  Anhydrides  of  Acids.  —  The  Action  of  Metals  on  Diluted 
Sulphuric  Acid. —  The  Neutralization  of  Sulphuric  Acid  by  Bases.  —  Com- 
parison of  the  Structure  of  Sulphuric  Acid  with  that  of  Water  and  of 
Hydrochloric  Acid.  —  Relationship  between  the  Amounts  of  Base  necessary 
to  form  the  Primary  and  Secondary  Sulphates.  —  Summary. 

HAPTER  X.  The  Atmosphere.  Physical  Properties 
of  the  Atmosphere.  The  Barometer.  Boyle's  Law 
and  Charles's  Law 66-71 

The  Weight  of  the  Atmosphere.  —  Calculation  of  Gas-volumes  to  Stan- 
dard Conditions. 

CHAPTER  XI.  The  Atmosphere  (Continued}.  Combus- 
tion in  Oxygen  and  in  Air  . .  .72-80 

Isolation  of  Nitrogen  from  the  Atmosphere.  —  Combustion  in  Oxygen 
and  Changes  of  Energy. —  Slow  Oxidation.—  Production  of  a  Flame.  — Re- 
versible Phenomena  of  Gaseous  Combustion.  —  General  Nature  of  the  Phe- 
nomena of  Combustion.  —  Enduring  Nature  of  Chemical  Energy.  —  Breathing 
Analogous  to  Combustion. 

CHAPTER  XII.  The  Atmosphere  (Continued}.  Composi- 
tion of  the  Atmosphere 81-87 

Estimation  of  the  Relative  Amounts  of  Oxygen  and  Nitrogen  in  the 
Atmosphere.  —  Other  Substances  Present  in  the  Atmosphere.  —  Summary  of 
Chapters  on  the  Atmosphere. 

CHAPTER  XIII.  The  Compound  of  Hydrogen  and  Ni- 
trogen. (Ammonia.) 88-97 

Preparation  and  Properties.  —  Decomposition  of  Ammonia  by  means  of 
Magnesium.  —  Isolation  of  Nitrogen  in  Ammonia.  —  Parallelism  between 
Ammonia,  Hydrogen,  Chloride,  and  Water. —  The  Volumetric  Composition 
of  Ammonia.  —  Changes  of  Energy  attending  the  Decomposition  and  Forma- 
tion of  Ammonia.  —  Decomposition  of  Water  and  Ammonia  by  Chlorine  ;  by 
Oxygen.  —  Summary. 


CONTENTS.  ix 

PAGE 

CHAPTER    XIV.      The   Compounds   of   Ammonia  -with 

Acids 98-105 

Resemblances  between  Potassium  Chloride  and  Ammonium  Chloride. 
—  Liberation  of  Ammonia  from  Ammonium  Chloride  and  Changes  of  En- 
ergy. —  Chemical  Character  of  a  Solution  of  Ammonia  in  Water.  —  Differ- 
ence between  Ammonium  and  Potassium  Salts.  — Summary. 

CHAPTER  XV.     The  Theory  which  Seeks  to  Explain  the 

Laws  of  Definite  and  Multiple  Proportions     .     .     .  106-122 

The  Definite  Composition  of  Chemical  Compounds.  —  The  Equivalent 
Weights  of  the  Metals. —The  Atomic  Theory. —Difficulty  of  determining 
the  Number  of  Atoms  combined  in  a  Molecule. —Practical  Advantages  of 
the  Atomic  Theory.  —  The  Formation  of  Compounds  from  the  Equivalent 
Weights  of  the  Elements.  —  Summary. 

CHAPTER  XVI.     Modern  Theory  of  the  Nature  of  Gases. 
Relation  between  Specific  Gravities  of  Gases  and 

their  Molecular  Weights 123-128 

Kinetic  Gas  Theory.  —  Summary. 

CHAPTER  XVII.     Determination  of  Atomic  Weights  by 

the  Use  of  the  Specific  Gravities  of  Gases     .     .     .  129-138 

The  Molecules  of  Hydrogen  consist  of  Two  Atoms. —The  Molecular 
Weight  of  Hydrogen  can  be  taken  as  the  Standard  for  measuring  other 
Molecular  Weights.  —  Determination  of  the  Maximum  Atomic  Weights  of 
the  Elements.  —  Determination  of  the  Number  of  Atoms  united  in  Mole- 
cules by  considering  the  Combining  Volumes  of  Gases.  —  Summary. 

CHAPTER  XVIII.     The  Expression  of  Chemical  Changes 

by  Formulae  and  Equations 139-148 

Composition  of  the  Molecules  of  Sulphur  Dioxide  and  Trioxide.  —  Rela- 
tive Atomic  Weights  of  Sodium  and  Potassium.  —  Neutralization  of  Hydro- 
chloric Acid.  —  Neutralization  of  Sulphuric  Acid,  and  Formation  of  Ammo- 
nium Chloride  in  Terms  of  the  Atomic  Theory.  —  Summary. 

CHAPTER  XIX.     Carbon 149-152 

Various  Modifications  of  Carbon;  Diamond;  Graphite. —Decompo- 
sition of  Animal  and  Vegetable  Substances.  —  Formation  of  Coke  ;  Charcoal ; 
Lamp-black. 

CHAPTER  XX.     Carbon  Dioxide 153-162 

Formula  for  one  Molecule  of  Carbon  Dioxide. — Preparation  and  Prop- 
erties of  Carbon  Dioxide.  —  Formation  of  Carbonates.  —  The  Primary  and 
Secondary  Carbonates  of  Potassium  and  of  Sodium.  —  Calcium  Carbonate, 
Magnesium  Carbonate,  and  Carbonate  of  Iron.  — Formation  of  the  Soluble 
Primary  Carbonate  of  Calcium  from  the  Insoluble  Secondary.  —  Summary. 


X  CONTENTS. 

PAGE 

CHAPTER  XXI.    Carbon  Monoxide  and  Methane.    (Hy- 

drogen  Carbide) 163-171 

Preparation  and  Properties  of  Carbon  Monoxide.  —  Reduction. — Me- 
thane. —  Occurrence.  —  Formation.  —  Preparation  and  Properties.  —  Deter- 
mination of  Chemical  Formula  of  Methane.  —  Summary. 

CHAPTER  XXII.     Substitution  of  Hydrogen  in  Methane 

by  Chlorine 172-184 

Substitution  of  Hydrogen  in  Metals.  —  Difference  between  the  Action 
of  Chlorine  and  of  the  Metals.  —  Methyl  Chloride.  —  Methylene  Chloride.— 
Methin  Chloride.  —  Atomic  Weights  of  Carbon  and  Chlorine. — Valence. — 
Summary. 

CHAPTER  XXIII.     The  Formation  of  Salts  by  Double 

Decomposition 185-194 

Formation  of  Salts  by  Substitution  and  Neutralization.  —  Salt  Forma- 
tion by  Action  of  an  Acid  on  a  Salt.  —  Double  Decomposition  between  Two 
Salts.  —  Causes  of  Double  Decomposition.  —  Electrolysis.  —  Formation  of 
Insoluble  Substances.  —  Neutralization  of  Bases  by  Acids.  —  Summary. 

CHAPTER  XXIY.  Chemical  Nature  of  Some  Other  Ele- 
ments and  Compounds  related  to  Those  which  have 
been  studied 194-205 

Elements  of  Chlorine,  Oxygen  and  Nitrogen  Families.  —  Hydrogen  Com- 
pounds of  Chlorine  and  of  Oxygen  Family.  —  Hydrogen  Sulphide,  Prepara- 
tion and  Properties.  —  Formation  of  Sulphides.  —  Hydrogen  Compounds  of 
Elements  of  the  Nitrogen  Family. 

LABORATORY  APPENDIX  .    206-284 


ELEMENTS  OF  CHEMISTRY. 


CHAPTER   I. 

CHANGES   IN    MATTER. 

Change  in  Matter.  All  matter  is  subject  to  change. 
In  some  cases,  for  example  when  a  piece  of  wood  is 
burning  or  when  water  is  flowing,  the  change  is  per- 
ceptible ;  in  other  cases  it  takes  place  too  slowly  to  be 
observed.  Instances  of  the  latter  kind  may  be  found 
in  the  wearing  away  of  a  rocky  mountain  along  the  bed 
of  a  stream,  or  in  the  gradual  decomposition  of  crystal- 
line rocks  into  other  and  different  materials  through 
the  influence  of  the  weather. 

Classification  of  Changes.  It  is  customary  to  classify 
those  alterations  which  are  superficial  and  transitory 
under  the  head  of  physics,  and  those  which  involve  a 
change  in  the  essential  properties  of  substance  under 
the  head  of  chemistry.  A  sharp  line,  however,  cannot 
be  drawn.  There  is  a  considerable  field  lying  along 
the  border  between  the  two  subjects  which  is  claimed 
by  both.  Operations  so  simple  as  the  dissolving  of 
salt  in  water,  probably  involve  a  chemical  change  as 
well  as  a  physical  one. 

1 


2  ELEMENTS   OF  CHEMISTRY. 

Observation  of  Changes.  From  the  earliest  times,  the 
instability  of  his  surroundings  attracted  the  attention 
of  man,  and  he  speculated  as  to  the  causes  of  the 
changes  going  on  around  him;  yet,  until  the  last  two 
hundred  years,  theories  regarding  chemical  phenomena 
were  not  based  on  scientific  observation.  The  essential 
difference  between  the  methods  of  thought  preceding 
the  eighteenth  century  and  those  of  modern  times  is, 
that,  during  the  earlier  period,  theories  concerning  struc- 
tural changes  in  matter  were  not  subjected  to  proof  by 
experiment.  During  the  later  period,  theories  have 
been  made  only  to  explain  facts  determined  by  the 
most  laborious  investigations.  In  consequence  of  the 
perverted  system  of  former  times,  little  progress  was 
made  toward  rationally  explaining  the  composition  of 
even  the  simplest  forms  of  matter.  During  the  first 
sixteen  centuries  of  the  Christian  era,  the  growth  of 
chemical  science  was  hopelessly  retarded,  first,  by  the 
theory  that  all  substances  were  composed  of  four  prin- 
ciples, —  earth,  water,  fire,  air  ;  and  second,  by  a  purely 
mercenary  aim,  —  the  hope  of  transforming  baser  metals 
into  gold. 

Superficial  and  Fundamental  Differences  in  Matter.  Cop- 
per and  zinc  when  melted  together  form  a  mass  (brass) 
similar  to  gold  in  appearance,  and  the  earlier  workers 
in  chemical  lines  supposed  this  alloy  to  be  a  some- 
what modified  gold.  Copper  when  heated  with  arsenic 
assumes  a  white  color,  and  the  resulting  substance  was 
believed  to  be  a  metal  which  differed  but  little  from 
silver.  Thus,  merely  superficial  qualities,  such  as  color, 
were  regarded  as  essential,  while  really  fundamental 
differences  between  various  forms  of  matter  were  un- 


CHANGES  IN  MATTER.  3 

observed.  We  now  know  that  although  brass  has  the 
color  of  gold,  it  nevertheless  is  entirely  different  from 
that  metal,  for  it  corrodes  when  heated,  or  when  brought 
in  contact  with  acids,  while  gold  does  not.  Copper  and 
zinc,  the  constituents  of  brass,  can  by  the  proper  means 
be  separated  from  the  alloy;  while  from  gold,  no  matter 
what  changes  the  metal  may  undergo,  nothing  but  gold 
has  ever  been  obtained.  A  given  volume  of  gold  has 
an  entirely  different  weight  from  the  same  volume  of 
brass.  It  has  a  different  melting  point ;  jn  fact,  in  all 
the  properties  which  we  now  recognize  as  essential,  the 
two  substances  are  distinct. 

Aims  of  Modern  Chemistry.  It  is  one  of  the  aims  of 
modern  chemistry  to  distinguish  accurately  between  the 
various  forms  of  matter,  and  to  discover  what  changes 
involve  an  alteration  in  the  nature  of  a  substance. 

The  advance  from  superficial  to  scientific  methods  of 
chemical  thought  was  not  brought  about  abruptly,  neither 
did  the  idea  that  experimentation  should  always  be  re- 
sorted to,  as  proof  of  a  theory,  immediately  find  adoption. 

The  Phlogiston  Theory.  At  the  beginning  of  the  eigh- 
teenth century,  a  chemist  (Stahl)  constructed  a  theory 
which  apparently  furnished  a  uniform  and  consistent 
explanation  of  a  common  chemical  phenomenon,  —  cqm- 
bustion.  According  to  this  theory,  any  substance  capa- 
ble of  burning  contained  an  element,  or  principle,  which 
was  called  phlogiston.*  This  principle  was  supposed 

*  At  one  time  phlogiston  was  considered  as  a  material  substance ;  at 
another,  as  merely  a  principle  devoid  of  weight.  Again,  it  was  identical 
with  the  element  at  present  called  hydrogen;  at  another  time  it  was 
supposed  to  have  negative  weight  (i.e.,  to  he  repelled  by  the  earth).  It 
was  also  looked  upon  as  the  principle  of  fire.  This  confusion  of  ideas  is 


4  ELEMENTS   OF  CHEMISTRY. 

to  pass  off  while  the  body  was  burning,  the  remainder 
being  "  dephlogisticated."  Charcoal,  for  example,  burns 
readily  and  leaves  a  small  quantity  of  ash.  During  the 
last  century  this  ash  was  considered  a  chemical  element 
which,  when  united  with  a  large  amount  of  phlogiston, 
formed  charcoal.  If  iron-rust  is  heated  with  charcoal, 
the  latter  substance  disappears,  while  iron  is  produced, 
mixed  of  course  with  the  ash.  The  iron-rust  was  there- 
fore supposed  to  take  up  the  phlogiston  from  the  char- 
coal, hence  iron  was  phlogisticated  iron-rust.  Although 
this  theory  was  false,  nevertheless  it  led  to  a  great  ad- 
vance in  the  science  of  chemistry,  because  it  indicated 
a  direction  in  which  new  work  could  be  conducted. 
During  the  eighty  years  following  its  establishment, 
greater  progress  was  made  than  during  the  preceding 
fifteen  centuries,  while  at  the  same  time  chemistry  as 
an  independent  science  began  to  be  followed  for  its  own 
sake.  Still,  investigators  of  the  "  phlogiston "  period 
had  not  entirely  outgrown  the  superficial  methods  of 
thought  belonging  to  their  predecessors.  Although  a 
marked  advance  had  been  made,  they  were  still  un- 
able, in  many  cases,  to  distinguish  with  sufficient  clear- 
ness essential  from  non-essential  phenomena.  Thus,  for 
example,  it  was  supposed  that  iron  in  burning  or  rust- 
ing gave  off  "  phlogiston,"  and  yet  the  rust  weighs 
more  than  the  iron.  True,  the  ash  of  the  charcoal 
weighs  much  less  than  the  charcoal  itself;  but  if  a  thor- 
ough investigation  of  the  combustion  of  that  substance 
were  undertaken,  the  weight  of  the  ash,  plus  that  of 
the  gaseous  products,  would  be  found  to  exceed  that 


sure  to  come  where  a  false  theory  is  called  upon  to  explain  a  large  class 
of  phenomena.  Perhaps  the  nearest  approach  to  "  phlogiston  "  in  mod- 
ern scientific  language  is  to  be  found  in  "  energy." 


CIIANGES IN 

of  the  original  charcoal.  This  essential  relation,  be- 
tween the  weight  of  a  burning  body  and  that  of  the 
bodies  produced  by  burning,  was  generally  ignored  dur- 
ing the  phlogiston  period.  It  is,  however,  of  such  fun- 
damental importance  that,  when  the  facts  were  finally 
recognized,  the  theory  which  overlooked  them  was  of 
necessity  abandoned.*  The  new  one  which  took  its 
place,  being  founded  solely  on  experimental  evidence, 
caused  a  much  greater  acceleration  in  the  already  rapid 
pace  at  which  chemistry  was  advancing.  In  order  to 
understand  clearly  the  reasons  for  such  a  radical  change 
of  views,  it  will  be  necessary  to  detail  one  or  two 
important  experiments. 

Lavoisier's  Experiments.  A  French  chemist,  Lavoisier, 
carefully  weighed  a  piece  of  tin,  placed  it  in  a  flask, 
hermetically  sealed  the  latter,  and  then  accurately  de- 
termined the  weight  of  the  whole.  He  afterward  kept 
the  flask  heated  during  a  period  of  some  weeks,  and 
observed  that  the  tin  had  changed  into  a  white  powder. 
At  the  same  time  the  flask  had  neither  gained  nor  lost 
in  weight,  and  consequently  no  phlogiston  could  have 
passed  off.  On  opening  the  vessel,  air  rushed  in  (a  par- 
tial vacuum  having  been  created),  and  the  total  weight 
was  greater  than  it  had  been  after  sealing.  Further- 
more, the  white  powder  weighed  more  than  the  original 
tin.  Lavoisier,  therefore,  came  to  the  conclusion  that 
the  tin,  when  heated,  took  up  one  of  the  constituents  of 
the  enclosed  air ;  that  the  diminution  in  volume  of  the 
air  was  connected  with  the  increase  in  weight  of  the  tin ; 

*  A  theory  as  to  the  cause  of  any  natural  phenomenon  must  of  neces- 
sity be  abandoned  as  soon  as  any  fact  is  discovered  which  contradicts 
that  theory. 


6  ELEMENTS   OF  CHEMISTRY. 

and  that  the  metal  did  not  give  off  phlogiston  when 
heated.  He  felt  sure  that  the  tin  took  up  a  constituent 
of  the  atmosphere,  but  he  could  not  at  that  time  give 
any  absolute  proof  of  his  theory,  because  that  portion  of 
the  air  which  is  absorbed  by  burning  substances  had 
not  as  yet  been  isolated.  By  a  strange  coincidence, 
the  chemical  theory  which  was  destined  to  overthrow 
that  of  phlogiston  was  finally  established  by  an  ardent 
adherent  of  the  phlogistic  school,  Joseph  Priestley,  who 
was  the  first  to  isolate  this  unknown  constituent  of  the 
air.  Priestley  demonstrated  that  red  precipitate,*  when 
heated,  yielded  mercury  and  gave  off  a  new  gas,  which 
he  called  dephlogisticated  air,t  but  which  Lavoisier  at 
once  recognized  as  that  part  of  the  atmosphere  which 
had  acted  on  the  tin.  The  alteration  in  the  metal  was 
analogous  to  combustion,  and  it  was  Priestley's  new  gas 
which  united  with  substances  when  they  burned.  Hav- 
ing come  to  this  conclusion,  Lavoisier,  by  repeating 
Priestley's  experiment  with  red  precipitate  (taking  the 
precaution  to  weigh  carefully  first  the  substance,  and 
then  the  resulting  gas  and  mercury  produced),  further 
succeeded  in  discovering  a  fundamental  law  of  natural 
science  which  reads  as  follows  :  — 

Law  of  the  Conservation  of  Matter.  During  chemical 
changes  the  amounts  of  matter  entering  into  such  changes 
remain  constant,  and  the  total  amount  of  matter  con- 
tained in  the  universe  never  varies.  From  this  it  fol- 
lows that  when  the  oxide  of  mercury  (red  precipitate) 
is  decomposed,  the  sum  of  the  weights  of  the  resulting 

*  Oxide  of  mercury. 

f  Called  dephlogisticated  air  because  substances  burned  in  it  more 
readily  than  in  common  air.  Dephlogisticated  air  could  contain  but 
little  phlogiston,  since  it  was  capable  of  taking  up  phlogiston  so  readily. 


CHANGES  IN  MATTER.  7 

oxygen  *  and  mercury  are  exactly  equal  to  the  weight 
of  the  original  substance.  The  tin  which  Lavoisier 
heated  in  a  flask  gained  in  weight,  but  this  gain  was 
exactly  balanced  by  the  loss  in  weight  of  the  air  en- 
dosed  in  the  vessel.  If  a  candle  were  burned  in  a 
scaled  glass  globe,  the  candle  would  apparently  disap- 
pear, yet  the  weight  of  the  globe  would  remain  unal- 
tered. The  chemical  compounds  at  first  present  in  the 
candle,  together  with  a  given  quantity  of  oxygen,  would 
have  rearranged  themselves  into  other  and  less  complex 
compounds,  differing  in  character  from  either  the  air  or 
the  candle,  but  the  total  amount  of  matter  would  have 
remained  the  same. 

Importance  of  Correct  Observation.  The  length  of  time 
which  it  took  to  come  to  the  conclusion  that  matter  is 
constant  in  quantity,  and  the  obstinacy  displayed  by 
the  adherents  of  phlogiston,  should  emphasize  for  us  the 
importance  of  careful  observation,  as  well  as  of  a  con- 
scientious weighing  of  all  the  facts  in  regard  to  a  given 
chemical  change,  before  we  venture  to  construct  any 
definite  theories  regarding  it. 

Importance  of  a  Knowledge  of  Facts.  In  undertaking  the 
study  of  any  science,  it  is  absolutely  essential  to  become 
acquainted  with  well-established  facts  before  undertak- 
ing to  understand  any  of  the  theories  which  have  been 
brought  forward  to  explain  the  existence  of  these  facts. 
We  must  also  remember  that  facts  remain  as  they 
are,  no  matter  what  theories  we  may  advance  for  their 
explanation.  Almost  invariably,  however,  exactly  the 
reverse  of  this  course  has  been  adopted.  As  a  result, 

*  The  name  given  to  the  gas  first  isolated  by  Priestley. 


8  ELEMENTS   OF  CHEMISTRY. 

students  acquire  the  opinion  that  chemical  science  is  a 
mere  collection  of  visionary  theories,  which  experimen- 
tation may  or  may  not  bear  out.  This  is  not  the  case. 
When,  for  example,  we  speak  of  atoms,  we  have  at  least 
as  exact  experimental  evidence  of  their  existence  as  the 
physicist  has  of  the  waves  which  he  discusses  in  the 
undulatory  theory  of  light.  Because  of  the  danger  of 
confusing  really  existing  things  with  those  which  are 
imaginary,  it  will  be  the  aim  of  this  book  to  discuss 
chiefly  facts,  leaving  the  theoretical  deductions  to  be 
made  from  them  for  a  larger  work. 


CHEMICAL   NOMENCLATURE. 


CHAPTER   II. 

CHEMICAL   NOMENCLATURE. 

THE  language  of  every  science  is  peculiar  to  itself ; 
advances  are  recorded  by  alterations,  and  history  is 
preserved  by  the  use  of  old  expressions.  In  order  to 
express  one's  self  properly  and  intelligently,  a  knowl- 
edge of  accepted  nomenclature  is  necessary.  An  ex- 
tended acquaintance  in  this  line  can  come  only  after 
considerable  experience,  still  it  is  not  out  of  place  to 
become  familiar  with  a  few  terms  in  chemistry  even 
prior  to  any  advance  in  the  study. 

Chemical  Elements.  Toward  the  end  of  the  last  cen- 
tury, the  idea*became  firmly  established  that  those  sub- 
stances which  cannot  be  decomposed  into  two  or  more 
simpler  ones,  having  entirely  different  properties,  are  to 
be  considered  as  chemical  elements.  This  term,  how- 
ever, must  not  be  understood  as  meaning  substances 
which  may  not  at  some  future  time  be  broken  down. 
Indeed,  past  experience  indicates  that  such  decomposi- 
tions will  be  brought  about  in  substances  now  classed 
as  elements.  An  example  of  such  an  experience  is 
found  in  the  history  of  the  substance  known  as  caustic 
potash,*  which  was  formerly  supposed  to  be  non-decom- 
posable, and  was  called  an  element.  Afterwards  it  was 
decomposed  into  a  metal  (potassium)  and  two  different 

*  Potassium  hydroxide. 


10  ELEMENTS   OF  CHEMISTRY. 

gases,  oxygen  and  hydrogen.  These  three  substances 
are  now  considered  elements ;  but  subsequent  experi- 
ment may  possibly  prove  these,  or  any  other  so-called 
elements,  to  be  compounds,  as  was  done  in  the  case  of 
caustic  potash. 

Number  of  Elements.  We  are  at  present  acquainted 
with  about  seventy  different  kinds  of  matter  which 
have  not  been  decomposed  into  two  or  more  simpler 
forms.*  Five  of  these  are  gases  at  ordinary  temper- 
atures and  pressures,  two  are  liquids,!  and  the  re- 
mainder are  solids.  These  substances  are  our  present 
chemical  elements. 

Classification  of  the  Elements.  Elements  can  be  roughly 
divided  into  two  great  classes ;  namely,  metals  and  not- 
metals.  The  most  pronounced  metals  are  malleable 
and  ductile,  are  good  conductors  of  electricity,  and 
have  a  so-called  metallic  lustre.  $  The  most  charac- 
teristic not-metals,  whether  gaseous,  liquid,  or  solid, 
are  neither  malleable  nor  ductile,  do  not  conduct  elec- 
tricity (or  at  least  are  poorer  conductors  than  the 
metals),  are  frequently  transparent  (oxygen,  nitrogen, 
sulphur  crystals)  or  translucent  (bromine,  iodine  in 
thin  sections),  and  they  have  no  metallic  lustre.  It 
is  a  matter  of  experience  that  the  most  pronounced 
metals  easily  form  stable  compounds  with  the  not- 

*  A  table  of  elements  will  be  found  at  the  end  of  the  book. 

t  A  third  element,  called  rubidium,  is  liquid  at  about  blood  heat,  and 
possibly  a  fourth  very  rare  element,  caesium,  may  be  liquid  when  it  is 
pure. 

J  An  appearance  like  that  of  the  most  familiar  polished  metals,  such 
as  silver,  gold,  brass,  etc.,  is  termed  a  metallic  lustre.  Substances  with 
metallic  lustre  are  not  transparent  or  translucent  except  in  the  very  thin- 
nest plates.  . 


CHEMICAL  NOMENCLATURE.  11 

metals,  but  no  absolute  prediction  as  to  the  behavior 
of  two  elements  toward  each  other  can  be  made,  even 
if  it  is  known  that  one  is  a  metal  and  the  other  a 
not-metal. 

Nomenclature  of  Compounds.  Compounds  containing 
but  two  elements  are  called  binary  ones.  In  the  no- 
menclature of  such  compounds,  the  termination  of  the 
name  of  one  element  is,  as  a  rule,  changed  to  -ide^  the 
name  of  the  other  remaining  unaltered. 

EXAMPLES  :  —  The  compound  of  iron  and  oxygen  is  called 
iron  oxide  or  oxide  of  iron. 

The  compound  of  hydrogen  and  sulphur  is  called  hydrogen 
sulphide  or  sulphide  of  hydrogen. 

The  compound  of  chlorine  and  sodium  is  called  sodium 
chloride  or  chloride  of  sodium. 

The  compound  of  phosphorus  and  oxygen  is  called  phosphorus 
oxide  or  oxide  of  phosphorus. 

The  same  element  may,  however,  enter  into  combina- 
tion with  a  series  of  others.  In  such  an  event,  it  is 
customary  to  form  for  the  series  a  class-name  taken 
from  that  of  the  element  which  all  of  the  members 
have  in  common,  the  termination  being  altered  to  -ide. 

EXAMPLES  :  —  Oxides  are  compounds  of  oxygen  with  other 
elements.  Sulphides  are  compounds  of  sulphur  with  other  ele- 
ments. Chlorides  are  compounds  of  chlorine  with  other  elements. 
Phosphides  are  compounds  of  phosphorus  with  other  elements. 

In  naming  such  a  series  of  compounds,  it  is  in- 
variably the  name  of  the  not-metallic  element,  or  of 
the  element  acting  like  a  not-metal,*  which  suffers  a 
change. 

*  Arsenic,  for  example,  is  an  element  which  frequently  acts  like  a  not- 
metal. 


xiara 


12  ELEMENTS   OF  CHEMISTRY. 

EXAMPLES  :  —  Sodium,  potassium,  and  iron  are  metals  ;  chlo- 
rine is  a  not-metal.  The  terms  sodium  chloride,  potassium 
chloride,  iron  chloride,  are,  therefore,  in  use,  while  the  expres- 
sions chlorine  sodide,  potasside,  or  ironide  are  inadmissible 
although  logically  just  as  correct  as  the  others. 

Where  the  binary  compound  is  formed  of  two  not- 
metals  or  two  metals,  then,  of  course,  convention  must 
settle  the  rules. 

EXAMPLES  :  —  We  speak  of  an  oxide  of  sulphur,  a  sulphide  of 
phosphorus,  a  chloride  of  iodine ;  yet  even  in  such  cases  it  is  the 
name  of  the  most  pronounced  not-metal  which  is  altered. 

Popular  Names.  It  must  be  remembered  that  not  a 
few  chemical  compounds  retain  the  names  which  were 
in  use  before  the  chemical  theories  of  the  present  cen- 
tury were  adopted,  and  that  some  have  since  that  time 
been  given  special  designations. 

EXAMPLES  :  —  Oxide  of  hydrogen  is  called  water ;  a  nitride  of 
hydrogen  is  called  ammonia;  a  phosphide  of  hydrogen  is  called 
phosphine. 

Chemical  Elements  and  Chemical  Compounds.  In  chemi- 
cal work  we  have  two  conditions  in  which  the  elements 
are  encountered.  The  first  is  that  of  the  elements  in 
"their  separate  and  individual  state,  the  second  that  of 
the  elements  united  in  compounds.  A  compound  dif- 
fers radically  in  behavior  and  properties  from  the  ele- 
ments of  which  it  is  composed.  A  chemical  compound 
is  not  a  mechanical  mixture  (as  sand  and  salt  would 
be) ;  for  the  mixture  has  properties  which  are  the 
mean  between  those  of  fits  constituent  parts,  while  the 
compound  has  110  res|eml)limce  to  its  components. 


WATER.  13 


CHAPTER  III. 

WATER. 

The  Physical  Properties  of  Water.  In  taking  up  the  sub- 
ject of  chemistry,  it  is  best  to  study  thoroughly  a  few 
chemical  bodies  and  the  changes  which  they  undergo. 
We  can  in  this  way  become  familiar  with  chemical 
phenomena  without  introducing  theories  which  are  apt 
to  give  the  impression  that  chemistry  is  a  visionary  and 
unreal  science.  Of  all  known  bodies,  water  is  the  one 
which  naturally  suggests  itself  for  first  consideration. 

Method  of  Study.  In  studying  this  substance  we  ex- 
amine first  its  physical  characteristics,  and  secondly  its 
chemical  characteristics. 

Physical  Properties  of  Water.  Water  is  a  liquid  substance, 
transparent  and  nearly  colorless  when  pure,  though  in  very  thick 
masses  it  apparently  has  a  deep  blue  color.  When  heated,  it 
expands ;  when  cooled,  it  contracts,  excepting  in  the  interval  ^>f 
temperatures  between  4°  and  0°,  *  *  where  exactly  the  reverse 
takes  place.  At  0°  pure  water  changes  to  ice,  and  the  ice,  fol- 
lowing the  usual  law,  continues  to  contract  as  the  temperature  is , 
lowered.  At  100°  f  water  boils,  and  then  changes  to  a  vapor,  J 
which  expands  regularly  when  further  heated. 

*  Throughout  the  book  temperatures  are  indicated  by  the  Centigrade 
thermometer. 

1  The  superior  numbers  in  the  text  refer  to  the  numbers  of  the  labor- 
atory notes  in  the  Appendix. 

t  At  the  standard  pressure  of  one  atmosphere  at  the  level  of  the  sea. 
This  standard  is  equal  to  a  pressure  of  760  millimetres  of  the  mercury 
barometer.  The  pupil  can  become  acquainted  with  the  structure  and 
uses  of  the  barometer  and  the  thermometer,  from  Note  1  of  the  Appendix. 

J  A  vapor  always  exists  in  the  presence  of  the  liquid  from  which  it  is 


14  ELEMENTS   OF  CHEMISTRY. 

Solutions.  Water  has  the  power  to  dissolve  a  large 
variety  of  other  substances  which  are  then  said  to  be 
in  solution.  Solutions  are  homogeneous  mixtures  of 
two  or  more  substances,  at  least  one  of  which  must  be 
a  liquid.* 

Solutions  of  Liquids  in  Liquids.  When  all  the  substances 
are  liquid,  then  the  following  special  cases  must  be  dis- 
tinguished: The  solution  may  take  place  in  any  pro- 
portion if  the  liquids  are  perfectly  miscible  (alcohol  and 
water),  or  the  liquids  may  only  partially  mix  (ether 
and  water).  In  either  case  it  is  not  proper  to  speak  of 
one  liquid  as  dissolving  another,  for  the  alcohol  has  just 
as  much  to  do  with  dissolving  the  water  as  the  latter 
has  with  dissolving  the  alcohol.  Where  one  liquic^  only 
partially  mixes  with  a  second,  it  is  also  true  that  the 
latter  will  take  up  an  equal  proportion  of  the  former. 
Not  infrequently  two  liquids,  when  brought  in  contact, 
will  not  mix  at  all  (oil  and  water). 

Solution  of  Solids  in  Liquids.  When  a  solid  dissolves  in 
a  liquid,  the  latter  can  take  up  only  a  certain  quantity 
called  a  maximum,  which  is  constant  for  constant  tem- 
peratures. In  the  case  of  any  given  solid,  this  maxi- 
mum of  weight  which  can  be  dissolved  in  a  liquid 

under  fixed  conditions,  is  called  its  solubility,!  and  the 

• 

formed.  When  the  temperature  is  high  enough  to  vaporize  the  liquid 
completely,  and  to  keep  it  vaporized,  we  use  the  term  gas  instead  of 
vapor. 

*  Two  or  more  gases  can  also  form  homogeneous  mixtures;  indeed, 
all  gases  are  perfectly  miscible ;  yet  such  mixtures,  being  formed  as  they 
are  without  change  in  the  total  volume  or  in  the  total  heat,  can  scarcely 
be  compared  with  ordinary  solutions. 

t  The  solubility  of  a  solid  is  expressed  either  in  percentage  by  weight 
of  solid  which  is  dissolved  in  100  parts  of  solvent,  or  in  percentage  by 
weight  which  is  dissolved  in  100  parts  of  solution. 


WATER.  15 

solution  is  said  to  be  "  saturated  "  ;   i.e.,  it  nas  taxen  up 
of  the  solid  all  that  it  can. 

As  a  rule,  the  solubility  of  a  solid  is  increased  by  increase  of 
temperature.  A  solution  which  is  saturated  at  a  given  tempera- 
ture will,  therefore,  be  unsaturated  at  a  point  above  this,  and, 
as  a  consequence,  will  take  up  more  of  the  solid.  On  the  other 
hand,  when  a  saturated  solution  cools,  a  separation  must  occur, 
as  the  solubility  of  the  solid  diminishes.* 

In  an  unsaturated  solution,  when  the  freezing  point 
is  reached,  the  water  t  will  separate  in  the  form  of  pure 
ice  until  the  unfrozen  solution  becomes  saturated ;  then 
the  solvent  and  the  dissolved  solid  will  separate  simul- 
taneously, sometimes  in  definite  relations  by  weight. 
The  solid  mixtures  which  are  formed  in  this  way  will 
have  definite  compositions,  and,  for  that  reason,  have 
sometimes  been  considered  as  chemical  compounds,  and 
have  received  the  special  name  of  cryohydrates.2 

Water  of  Crystallization.  Not  infrequently  substances 
separate  in  the  form  of  crystals  from  solutions  in  water,  t 
These  crystals  often  contain  a  definite  quantity  of  water 
for  a  definite  weight  of  solid.  The  form  of  the  crystal, 
as  well  as  the  relative  amount  of  water,  never  varies 
for  the  same  substance  under  the  same  conditions. 
The  water  which  is  so  combined  to  form  a  solid  crystal 
is  called  water  of  crystallization.  Compounds  formed 

*  Generally  the  solid  separates  in  a  definite  geometric  form,  with 
plane  faces  which  have  a  uniform  angle  with  each  other.  The  process 
is  then  called  crystallization,  and  the  solid  so  formed  is  a  crystal. 

t  Provided  the  solvent  is  water.  The  phenomena  are  the  same  with 
any  other  liquid,  provided  it  be  capable  of  freezing  within  the  limits  of 
the  experiment.  In  the  case  of  a  liquid  like  alcohol,  which  does  not 
freeze,  the  cooling  of  course  goes  on  until  the  solution  is  saturated,  then 
separation  begins. 

|  The  same  is  true  of  a  number  of  other  solvents. 


16  ELEMENTS   OF  CHEMISTRY. 

between  a  substance  and  its  water  of  crystallization  can 
be  easily  broken  down.  Sometimes  the  water  passes 
off  even  at  ordinary  temperatures,  and  the  substance 
crumbles  to  a  powder  (soda  crystals)  ;  sometimes  the 
temperature  must  be  raised  to  the  boiling  point  of 
watery  or  even  above  this,  in  order  to  produce  the 
same  result  (alum  crystals).  A  number  of  cases  are 
known  in  which  a  portion  of  the  water  cannot  be 
driven  off,  even  if  the  temperature  is  increased  far  be- 
yond the  boiling  point ;  but  a  careful  investigation  of 
these  exceptions  proves  that  water  is  no  longer  present 
as  such,  but  has  been  broken  down  to  enter  into  an 
entirely  new  class  of  compounds.  True  water  of  crys- 
tallization is  always  easily  expelled.3 

Efflorescence  and  Deliquescence.  Substances  which  lose 
a  part  of  their  water  of  crystallization  at  ordinary  tem- 
peratures are  efflorescent  (soda  crystals,  copper  sulphate 
crystals).  On  the  other  hand,  bodies  are  known  which 
greedily  absorb  moisture  when  they  are  brought  in  con- 
tact with  it,  sometimes  attracting  enough  liquid  to 
dissolve  them.  Such  bodies  are  deliquescent.4" 

Anhydrous  and  Hydrated  Crystals.  It  must  always  be 
remembered  that  crystals  need  not  necessarily  contain 
water  of  crystallization  (diamond,  chromate  of  potas- 
sium, nitrate  of  silver,  and  saltpetre)  ;  indeed,  by  far 
the  greater  part  do  not.  Substances  which  contain  no 
water  of  crystallization  are  said  to  be  anhydrous  ;  those 
with  it,  Jiydrated. 

Solutions  of  Gases  in  Liquids.  There  is  as  great  a  va- 
riation in  the  solubility  of  gases  as  there  is  in  that  of 


solids  and  liquids,  some  being  very  readily  dis'solved 
(ammonia,  hydrochloric  acid)  ;  some  less  readily  (chlo- 
rine) ;  others  with  great  difficulty  (hydrogen).  With 
one  or  two  exceptions,  the  solubility  of  gases  diminishes 
as  the  temperature  of  the  solvent  increases.  An  in- 
crease of  the  pressure  to  which  a  gas  is  subjected  brings 
with  it  a  corresponding  increase  in  the  solubility  of  the 
gas.  When  the  pressure  is  removed,  the  dissolved  gas 
passes  off  until  the  normal  solubility  at  the  temperature 
and  pressure  of  the  atmosphere  is  reached.*  The  solu- 
bility of  a  gas  varies  directly  as  the  pressure.5 

Impurities  in  Water.  Distillation.  The  impurities  found 
in  water  are  either  mechanically  suspended  or  dissolved. 
The  suspended  impurities  can  be  removed  by  filtration,! 
the  dissolved  ones,  in  certain  cases,  by  distillation.  Dis- 
tillation consists  in  heating  the  solvent  to  its  boiling 
point  in  an  apparatus  suitably  arranged  for  collecting 
and  condensing  the  vapors  in  a  separate  vessel.  Where 
the  substances  dissolved  are  solid,  they  are  in  most 
cases  $  removed  by  this  process.  Liquid  substances 
dissolved  in  water  can  be  removed  by  distillation  only 
when  the  boiling  point  of  the  liquid  is  much  above  or 
below  that  of  water ;  for,  unless  this  be  the  case,  a  por- 
tion of  one  liquid  will  always  vaporize  with  the  other. 
Even  where  there  is  a  considerable  interval  between  the 
boiling  points,  the  operation  of  distilling  must  be  re- 


*  The  effervescing  of  soda-water  is  an  illustration  of  this  phenomenon. 
The  gas,  carbon  dioxide,  is  forced  to  dissolve  in  the  water  by  great  pres- 
sure. When  the  pressure  is  removed,  the  carbon  dioxide  must  escape. 

t  By  passing  the  water  through  a  porous  substance ;  for  instance,  espe- 
cially prepared  blotting-paper  or  unglazed  porcelain. 

\  Certain  solid  substances  vaporize  with  the  water.  £uch  substances 
cannot,  of  course,  be  removed  by  ordinary  distillation. 


18  ELEMENTS   OF  CUEMISTltT. 

peated  several  times,  the  lower  and  higher  boiling  por- 
tions being  collected,  separated,  and  then  again  distilled 
from  separate  vessels.  This  operation  is  called  fractional 
distillation. ,6 

Natural  Waters.  Natural  waters  are  all  more  or  less 
impure.  Rain-water  or  melted  snow  is  nearest  to  abso- 
lute purity,  but  even  this  contains  solid  and  gaseous 
substances  collected  in.  passing  through  the  atmosphere. 
When  rain-water  soaks  through  the  soil,  it  takes  up  a 
certain  portion  of  the  solid  substances  with  which  it 
comes  in  contact.  If  poisonous  substances  in  the  soil 
or  organisms  Deleterious  to  life  are  taken  up,  the  water 
will  be  unfit  for  drinking  purposes ;  and  this  is  some- 
times the  case  in  well  -or  spring  water.  Where  certain 
constituents  of  the  soil  are  of  an  extremely  soluble 
nature,  like  common  salt,  Epsom  salt,  etc.,  they  are  of 
course  taken  up  by  the  water  which  filters  through. 
Where  such  a  water  escapes  from  the  soil,  it  produces 
mineral  springs.  Naturally  the  impurities  dissolved  in 
well  or  spring  water  vary  with  the  nature  of  the  soil 
through  which  the  rain-water  forming  the  well  or  spring 
has  trickled. 


WATEE.  19 


CHAPTER  IV. 

WATER  (Continued-}. 

THE  first  inquiry  into  the  chemical  nature  of  water 
should  have  for  its  object  the  definite  solution  of  the 
question  whether  water  is  a  chemical  element  or  a  com- 
pound,* and  in  order  to  find  an  answer  we  must  resort 
to  experiment.!  At  the  same  time,  it  will  be  possible, 
by  the  study  of  a  few  facts,  to  get  a  clearer  conception 
of  what  is  actually  meant  by  a  chemical  element. 

Action  of  Sodium  and  Potassium  in  Water.  If  a  piece 
of  the  metal  sodium  is  placed  in  contact  with  water,  an 
instantaneous  change  takes  place ;  the  sodium  becomes 
hot,  it  melts,  and  the  globule  of  metal  will  move  rap- 
idly round  on  the  surface  of  the  water. t  If  the  water 
is  thickened  with  starch  paste  so  that  this  movement 
cannot  take  place,  the  heat  developed  will  finally  pro- 

*  See  page  8. 

t  In  former  times  water  was  regarded  as  an  element.  One  reason  for 
this  was  that  water  is  so  common,  and  it  appears  to  be  generated  during 
so  many  chemical  processes  (for  instance,  the  combustion  or  distillation 
of  wood).  The  chief  means  for  decomposing  substances  which  the  older 
chemists  had  at  their  disposal  was  the  action  of  fire.  Certainly  no 
temperature  which  they  could  produce  would  destroy  water,  and  this 
was  another  reason  for  supposing  it  to  be  an  element.  We  should  our- 
selves be  compelled  to  regard  water  as  an  element  were  we  not  able  to 
decompose  it  into  two  different  substances. 

\  The  specific  gravity  of  sodium  is  less  than  that  of  water;  .that  is,  a 
given  bulk  of  water  would  weigh  more  than  the  same  bulk  of  sodium. 
The  sodium,  therefore,  floats  on  water. 


20  ELEMENTS   OF  CHEMISTRY. 

duce  a  flame  which  is  caused  by  the  burning  of  a  gas 
which  is  passing  off.  That  such  a  gas  is  really  liberated 
is  easily  proved  by  placing  the  piece  of  sodium  in  a  wire 
net,  and  inverting  over  this  a  tube  closed  at  one  end,  and 
filled  completely  with  water.  The  gas  will  rise  in  bub- 
bles, and,  if  the  original  quantity  of  the  sodium  was 
sufficient,  will  entirely  fill  the  tube.  If  the  latter  is 
now  removed,  mouth  downward,  and  held  over  a  flame, 
the  gas  will  take  fire,  and  burn  up  completely  when 
the  tube  is  inverted.  Essentially  similar  phenomena 
will  be  observed  if  the  metal  potassium  *  is  substituted 
for  sodium,  except  that  the  change  is  much  more  vio- 
lent. The  gas  bursts  into  flame  even  when  the  water 
has  not  been  previously  thickened  with  starch  paste. 
The  color  of  the  flame  with  sodium  is  yellow,  with  po- 
tassium bluish-violet;  and  to  a  superficial  observer  it 
might  appear  that  the  gas  given  off  by  potassium  and 
water  is  different  from  that  produced  by  sodium  and 
water.  That  this  is  not  the  case,  however,  can  be 
shown  by  comparing  the  flame  of  the  gas  collected  in 
a  test-tube  from  sodium  with  that  collected  from  potas- 
sium. In  both  cases  the  flame  will  be  nearly  color- 
less.7 

The  yellow  and  the  violet  colors  are  due  to  something  derived 
from  the  potassium  and  the  sodium.  The  explanation  is  that 
small  particles  of  the  metals  are  carried  up  into  the  flame,  and, 
being  heated  to  incandescence,  give  off  the  colored  light  peculiar 
to  each. 

*  Potassium  is  a  metal  very  much  like  sodium  in  appearance  and 
character.  Its  specific  gravity  is  less  than  that  of  water,  therefore  it 
floats.  Both  sodium  and  potassium  are  soft>  can  he  easily  cut  with  a 
knife,  and  the  freshly  cut  surfaces  possess  a  brilliant  metallic  lustre, 
which  almost  instantly  disappears  on  exposure  to  the  air.  Because  they 
are  so  easily  altered  hy  exposure  to  the  air,  they  must  be  preserved  under 
petroleum. 


WATER.  21 

Nature  of  the  Action  of  Sodium  and  Potassium  on  Water. 
Is  the  gas  which  is  developed  in  this  process  due  to  a 
breaking  down  of  the  water,  or  does  it  come  from  the 
potassium  and  the  sodium?  Either  view  seems  plaus- 
ible ;  and,  indeed,  had  the  two  metals  in  question  been 
known  in  the  last  century,*  the  latter  interpretation 
of  the  change  would  undoubtedly  have  been  the  one 
adopted.  Sodium  and  potassium  would  have  been  re- 
garded as  compound  substances,  and  it  would  have  been 
supposed  that  they  gave  up  a  gas  (phlogiston)  when 
brought  into  contact  with  water.  The  substances, 
therefore,  which  remained  behind,  dissolved  in  the 
water  (caustic  soda  and  caustic  potash),  would  have 
been  classed  as  elements.  Such  an  explanation  is  en- 
tirely incorrect,  however,  for  the  gas  does  not-  come 
from  the  potassium  or  the  sodium.  It  results  from 
the  breaking  down  of  water  into  two  parts,  one  of 
which  passes  off  as  a  gas,  while  the  other  unites  with 
the  potassium  or  sodium  to  form  a  new  compound  body, 
which  dissolves  in  the  water.  That  this  is  really  the 
case  is  shown  by  the  following  experiments :  — 

Decomposition  of  Water  by  the  Electric  Current.  If 
water  t  is  placed  in  a  cup,  into  the  bottom  of  which 
two  pieces  of  platinum  foil  are  placed  in  such  a  man- 
ner that  they  can  be  connected  with  the  two  poles  of 
an  electric  battery,  and  an  electric  current  is  passed 
through  the  water,  bubbles  of  gas  will  appear  at  both 
pieces  of  foil.  If  a  tube,  closed  at  one  end  and  filled 

*  Sodium  was  discovered  in  1807  by  Davy ;  potassium,  in  1808,  by  the 
same  investigator. 

t  Rendered  slightly  acid  by  means  of  sulphuric  acid ;  pure  water  does 
not  conduct  electricity. 


22  ELEMENTS   OF  CHEMISTRY. 

with  water,  is  inverted  over  each  piece  of  foil,  the  gases 
can  easily  be  collected.  It  will  then  be  found  that  the 
water  in  one  tube  is  expelled  more  rapidly  than  in  the 
other.  If  the  tubes  selected  are  of  the  same  size,  one 
will  be  exactly  filled  with  gas  at  the  moment  when  the 
other  is  only  one-half  full.8  It  is  evident,  then,  that 
water  decomposes  into  two  gases,  one  of  which  separates 
at  the  positive,  the  other  at  the  negative  pole ;  and  it  is 
also  true  that  there  is  about  twice  as  much  of  one  gas 
as  of  the  other.  If  the  tube  containing  the  greater 
quantity  *  is  removed,  and  brought  in  contact  with  a 
flame,  the  gas  will  be  found  to  burn  with  a  flame  iden- 
fcieal  in  appearance  with  the  one  observed  during  the 
combustion  of  the  gas  produced  from  sodium  and  po- 
tassium. It  is  probable,  therefore,  that  the  gas  lib- 
erated when  experimenting  with  those  metals  had  its 
origin  in  the  water  with  which  they  were  brought  in 
eontact,  and  that  it  did  not  come  from  the  metals 
themselves. f 

The  proof  that  the  gas  which  is  formed  by  the  action 
of  sodium  or  potassium  on  water  does  not  come  from 
the  metal,  but  that  it  has  its  origin  in  the  water  which 
is  decomposed,  has  also  been  obtained  by  other  methods. 
These,  however,  would  involve  more  difficult  experi- 
mentation than  is  possible  for  beginners.  It  has  been 

*  Experimentation  will  show  that  this  has  been  collected  at  the 
negative  pole  of  the  battery.  It  is,  therefore,  the  electro-positive  con- 
stituent. 

f  The  proof  that  the  gases  obtained  by  the  action  of  sodium  or  potas- 
sium on  water,  and  the  gas  collecting  at  the  negative  pole  when  water 
is  decomposed  by  the  electric  current,  are  really  identical  has  not  been 
shown  by  the  experiments  which  have  been  given.  The  only  point 
made  use  of  is  that  they  both  burn  with  a  similar  flame.  Something 
more  than  this  is  necessary  before  we  can  really  be  satisfied  as  to  their 
identity.  This  proof  is  found  in  the  fact  that  the  gas  from  both  sources, 
when  burned,  forms  the  same  substance;  namely,  water  (see  page  27). 


WATER.  23 

shown  that  the  sum  of  the  weights  01  the  sodium  used 
and  of  the  water  decomposed  is  equal  to  the  sum  of 
the  weights  of  the  gas  produced  and  of  the  compound 
of  sodium  which  remains  dissolved.  If  all  excess  of 
water  is  removed  by  heat,  then  the  sodium  compound 
remaining  weighs  more  than  did  the  sodium  originally 
used.  The  sodium,  therefore,  could  not  have  given  off 
the  gas,  for  in  that  event  it  would  have  diminished  in 
weight. 

That  the  volume  of  one  of  the  gases  into  which  water 
is  broken  down  is  exactly  twice  as  great  as  that  of  the 
other  gas  cannot  be  proved  from  the  decomposition  of 
water  by  the  electric  current,  since  the  method  employed 
is  not  sufficiently  accurate.  A  more  careful  and  ex- 
tended study  of  the  composition  of  water  by  other 
means  is  necessary  to  show  that  the  ratio  of  the  two 
gases  by  volume  is  exactly  2:1. 

Sodium  and  Potassium  are  Elements ;  Water  is  a  Compound. 
A  number  of  observations  similar  to  the  ones  just  given, 
and  involving  the  action  of  sodium  and  potassium  on 
other  substances  which  are  chemically  like  water,  have 
brought  us  to  the  conclusion  that  sodium  and  potassium 
are  not  decomposable.  In  all  cases  of  experiment,  when 
a  theory  that  these  metals  are  decomposed  into  simpler 
substances  might  seem  plausible,  closer  analysis  will 
show  that  it  is  not  sodium  or  potassium  that  is  broken 
down,  but  the  other  substances  with  which  these  metals 
are  brought  in  contact.  Sodium  and  potassium  are, 
therefore,  elements,  and  water  is  a  compound.  Having 
settled  this,  the  next  step  is  to  discover  what  and  how 
many  dissimilar  substances  can  be  produced  by  the  sep- 
aration of  the  water  into  its  constituent  parts. 


24  ELEMENTS   OF  CHEMISTRY. 

Hydrogen  and  Oxygen.  We  have  seen  that  when  an 
electric  current  is  passed  through  water,  a  gas  separates 
both  at  the  positive  and  at  the  negative  pole  (see 
page  22).  The  accumulation  at  the  latter  is  twice  as 
great  as  that  at  the  former,  and  the  question  at  once 
arises :  are  the  gases  identical,  or  do  they  differ  from 
each  other?  To  all  appearances  they  are  alike,  both 
are  colorless,  neither  possesses  an  odor;  yet  a  distinc- 
tion will  at  once  become  apparent  if  a  lighted  taper  is 
applied  to  each  in  turn.  The  one  which  has  been  col- 
lected at  the  negative  pole  burns  with  a  flame  identical 
in  appearance  with  that  shown  by  the  gas  obtained  from 
the  action  of  sodium  or  potassium  on  water.  Indeed, 
as  we  have  seen,  it  is  in  reality  the  same  substance. 
This  gas  is  termed  hydrogen.*  The  gas  collected  at  the 
positive  pole  does  not  burn,  but  it  causes  a  taper  placed 
in  it  to  burn  much  more  energetically  than  it  would  in 
the  air.  Even  if  the  taper  has  but  a  feeble  spark,  it 
will  burst  into  flame.  This  gas  is  called  oxygen.9 

Formation  of  Water  from  Hydrogen  and  Oxygen.  It  has 
been  shown  that  hydrogen  and  oxygen  can  be  obtained 
from  water ;  can  water  also  be  produced  from  these  sub- 
stances? Because  if  it  can,  then  these  two  elements 
alone  make  up  the  compound,  water.  The  following 
experiment  will  demonstrate  this  fact:  - 

A  tube,  sealed  at  one  end,  is  filled  with  mercury,  then 

*  Neither  of  the  methods  which  have  heen  discussed  are  expedient 
for  the  preparation  of  the  considerable  quantities  of  hydrogen  necessary 
for  ordinary  laboratory  purposes.  To  accomplish  this  end  another  way 
is  necessary,  which  is  described  in  Experiment  9,  Appendix.  Both  oxy- 
gen and  hydrogen  are  called  elements;  for  no  experiments  have  been 
discovered  by  means  of  which  these  forms  of  matter  can  be  separated 
into  two  or  more  different  substances  as,  for  example,  has  been  done  in 
the  case  of  water. 


WATER.  25 

closed  at  the  other  end  by  the  thumb,  and  inverted  over 
a  trough  filled  with  the  same  liquid.  Perfectly  pure 
hydrogen  is  then  run  into  the  tube  until  the  latter  is 
filled  for  about  five  centimetres.*  Oxygen  is  added  so 
that  its  bulk  is  approximately  two  centimetres,  and  the 
tube  is  firmly  closed.  The  tube  used  in  this  experi- 
ment has  two  short  platinum  wires  fused  through  its 
sides  near  the  closed  tip.  These  are  connected  with 
the  two  short  poles  of  an  induction  coil,  and  a  spark  is 
allowed  to  pass  through  the  mixture  of  gases.  A  bright 
flash  is  seen,  a  slight  explosion  is  heard,  and  the  mercury 
rises  in  the  tube.  A  portion  of  the  gas  will  remain,  and 
this  will  be  found  to  have  the  properties  of  hydrogen. 
All  the  oxygen  with  a  part  of  the  hydrogen  has  been 
used  to  form  water.  If  the  tube  is  carefully  marked 
in  cubic  centimetres,  so  that  the  volumes  of  the  gases 
which  were  introduced  can  be  accurately  measured,  it 
can  easily  be  proved  that  the  contraction  in  total  volume 
is  such  that  exactly  two  volumes  of  hydrogen  have  united 
with  one  of  oxygen  to  form  water.10  t 

A  mixture  of  hydrogen  and  oxygen  remains  without 
change  indefinitely  under  ordinary  conditions,  union 
only  taking  place  if  a  lighted  taper  is  brought  in  contact 
with  the  gases,  or  if  an  electric  spark  is  passed  through 
the  mixture.  An  explosion  which  may  be  violent  will 
then  result,  provided  the  proportions  in  which  the  gases 
taken  are  nearly  two  parts  by  volume  of  hydrogen  to 
one  of  oxygen. 

*  For  the  preparation  of  pure  hydrogen,  see  Experiment  9,  Appendix. 

t  Of  course  the  amount  of  water  which  can  be  formed  in  a  small  glass 
tube  is  too  little  for  identification  as  such.  In  order  to  prove  that  water 
is  really  the  product  of  the  action  of  hydrogen  on  oxygen,  a  large  quantity 
of  hydrogen  must  be  burned  in  oxygen.  In  order  to  be  able  to  furnish 
this  proof,  the  pupils  should  perform  the  experiment  given  in  Note  12  of 
the  Laboratory  Appendix. 


26  ELEMENTS   OF  CHEMISTRY. 

Relation  between  the  Volumes  of  Hydrogen  and  Oxygen, 
and  of  the  Water  Produced.  If  exactly  two  volumes 
of  hydrogen  and  one  of  oxygen  are  exploded  in  the 
apparatus  described  in  the  preceding  paragraph,*  the 
mercury  will  completely  fill  the  tube,  because  the  vol- 
ume of  liquid  water  which  is  formed  is  inconsiderable, 
compared  with  the  volume  of  the  gases  from  which  it 
has  been  produced.  But  if  the  tube  which  contained 
the  hydrogen  and  oxygen  is  kept  heated  by  a  steam- 
jacket,  so  that  its  temperature  is  that  of  the  boiling 
point  of  water,  then  the  water  vapor  produced  will 
not  only  occupy  a  visible  portion,  but  this  volume  will 
be  exactly  two-thirds  of  that  taken  up  by  the  gases 
before  explosion.11  The  facts  which  have  been  dis- 
covered are,  therefore,  as  follows :  Hydrogen  and  oxy- 
gen unite  chemically  to  form  a  new  substance,  which  is 
water.  This  substance  is  produced  by  the  interaetion 
of  exactly  two  volumes  of  hydrogen  and  one  of  oxygen. 
The  volume  of  the  vapor  of  this  compound  is  exactly 
two-thirds  of  the  sum  of  the  volumes  of  the  original 
gases  from  which  it  is  formed.  If  more  than  two  vol- 
umes of  hydrogen  to  one  of  oxygen  have  been  mixed 
before  the  explosion,  then  some  hydrogen  will  remain 
unaltered ;  if  more  than  one-half  as  much  oxygen  as 
hydrogen  by  volume  was  present,  then  some  oxygen 
will  be  found  in  the  tube  after  the  explosion.  No 
matter  in  what  proportions  hydrogen  and  oxygen  are 
mixed,  they  will  unite  to  produce  water  only  in  the 
proportion,  two  of  hydrogen  to  one  of  oxygen. 

Relation  of  Hydrogen  to  Oxygen  by  Weight.  Obviously 
a  given  volume  of  hydrogen  must  always  have  the  same 

*  For  an  exact  description  of  this  apparatus,  see  Note  10,  Laboratory 
Appendix. 


WATER.  27 

no  matter  where  it  is  found,  provided  the  condi- 
tions of  temperature  and  barometric  pressure  remain 
identical,*  and  the  same  must  also  be  true  of  a  given 
volume  of  oxygen.  Hence,  it  follows  from  the  above 
experiments  that  water  is  always  produced  by  the  inter- 
action of  hydrogen  and  oxygen  in  a  certain  definite  ratio 
by  weight.  This  ratio  can  be  discovered  by  weighing  a 
glass  globe  which  has  been  emptied  by  means  of  an  air- 
pump,  weighing  the  same  after  filling  it  with  pure 
hydrogen,  then  removing  the  hydrogen,  filling  the  globe 
with  oxygen,  and  again  weighing.  Comparing  the  re- 
sults, we  shall  have  the  relation  existing  between  the 
weight  of  a  given  volume  of  hydrogen,  and  that  of 
the  same  volume  of  oxygen.  This  relation  has  been 
found  to  be  as  one  to  sixteen  ;  or,t  in  other  words,  if  the 
specific  gravity  of  hydrogen  is  placed  at  unity,  the  spe- 
cific gravity  of  oxygen  is  sixteen.  But  we  have  learned 
that  two  volumes  of  hydrogen  unite  with  one  of  oxygen 
to  form  water;  hence,  the  relationship  by  weight  be- 
tween the  hydrogen  and  oxygen  which  form  water  is  as 
two  to  sixteen,  or  one  to  eight. $ 

One  fact  still  remains  to  be  shown,  for  we  have  not 
yet  definitely  proved  that  the  product  of  the  explosion 
between  hydrogen  and  oxygen  really  is  water.  The 
quantity  of  the  latter  substance  obtainable  by  the 
method  we  have  employed  is  so  small  that  it  could 
not  practically  be  identified.  However,  all  doubts  on 
this  subject  can  be  removed  by  arranging  a  hydrogen 

*  See  pages  67,  68,  69. 

f  I.e.,  if  the  volume  of  the  globe  was.such  as  to  hold  exactly  one  gram 
of  hydrogen  under  the  conditions  of  the  experiment,  then  the  oxygen 
would  weigh  sixteen  grams.  The  same  ratio  would  be  preserved,  no 
matter  what  was  the  weight  of  the  original  volume  of  hydrogen. 

|  Throughout  this  book  proportions  are  given  by  weight  unless  vol- 
ume is  expressly  stated. 


28  ELEMENTS  OF  CHEMISTRY. 

apparatus  which  will  deliver  pure,  dry  hydrogen  through 
a  jet,*  lighting  the  gas,  and  then  plunging  the  jet  into 
a  jar  filled  with  oxygen.  It  will  continue  to  burn  more 
energetically  than  in  the  air,  and  drops  of  water  pro- 
duced by  the  combustion  will  soon  collect  on  the  sides 
of  the  vessel.12  Experiment  has  shown  that,  no  matter 
what  the  origin  of  the  hydrogen  may  be,  it  always  pro- 
duces water  whenever  it  is  burned  in  oxygen. 

Summary.  The  facts  which  we  have  now  learned  in 
regard  to  the  chemical  nature  of  water  can  be  summed 
up  as  follows  :  — 

1.  When  sodium  or  potassium  are  brought  in  contact 
with  water,  a  gas,  hydrogen,  is  given  off  from  the  water. 

2.  Considerable  heat  is  developed  during  the  process, 
the  sodium  melting,  and,  if  kept  stationary,  even  setting 
fire  to  the  hydrogen,  while  the  gas  passing  from  the 
potassium  takes  fire  even  if  the  metal  is  moving. 

3.  Water  can  be  decomposed  by  the  electric  current, 
hydrogen  and  a  second  gas,  oxygen,  being  produced  by 
the  process. 

4.  The  ratio  by  volume  between  these  gases  when 
they   are    formed   from   water   is   as    two   volumes   of 
hydrogen  to  one  of  oxygen. 

5.  Water  can  be  produced  from  hydrogen  and  oxy- 
gen by  exploding  a  mixture  of  the  two  gases. 

6.  Water  is  the  result  of  the  union  of  exactly  two 
volumes  of  hydrogen  and  one  volume  of  oxygen. 

7.  Water  is  formed  by  the  union  of  two  parts   by 
weight  of  hydrogen  with  every  sixteen  of  oxygen.f 

8.  Hydrogen  being  selected  as  the  standard,  the  specific 
gravity  of  oxygen  is  sixteen. 

*  See  Experiment  9,  Appendix.        f  In  exact  numbers,  2  : 15.88. 


PRODUCTS  OF  ACTION  OF  SODIUM,   ETC.         29 


CHAPTER   V. 

THE    PRODUCTS    OF    THE   ACTION   OF   SODIUM 
AND   POTASSIUM   ON   WATER. 

Caustic  Soda  and  Caustic  Potash.  When  sodium  or  po- 
tassium is  brought  in  contact  with  water,  we  have  seen 
that  both  metals  dissolve,  while,  at  the  same  time,  heat 
is  given  off.  We  have  further  learned  that  the  hydro- 
gen wjiich  is  produced  is  a  constituent  of  the  water. 
What  becomes  of  the  sodium  or  potassium?  Appar- 
ently they  have  disappeared,  and  the  water  feel%  soapy. 
If  the  liquid  in  which  the  metals  were  dissolved  is 
evaporated,  there  will  remain,  in  each  case,  a  white, 
semizsolid  deliquescent  *  mass,  which  will  readily  harden 
when  heated  to  about  150*  c^tigrade.  Owing  to  the 
fact  that  these  substances  win  burn  the  skin  and  mu- 
cous membrane,  and  that  they  contain  hither  sodium  or 
potassium,  they  are  called  caustic  soda  and  potash, 
respectively.13 

Electrolysis  of  Caustic  Soda  or  Caustic  Potash.  Put  one 
of  these  solids  into  a  small  platinum  dish,  mix  with  it 
a  little  water,  f  and  connect  the  mass  with  the  negative 
pole  of  a  powerful  battery,  while  the  dish  is  joined  to 
the  positive.  The  liquid  will  become  warm,  bubbles  of 
gas  will  escape,  and  globules  of  a  metallic  substance  will 
appear  at  the  top  of  the  wire.  These  can  be  scraped 

*  See  page  16.  t  Not  enough  to  dissolve. 


SO  ELEMENTS  OF 

off.  They  corrode,  and  even  may  take  fire  in  moist  air. 
They  decompose  water,  yielding  hydrogen.  In  short, 
they  possess  all  of  the  properties  belonging  to  sodium 
or  potassium.  We  have  thus  proved  that  when  sodium 
or  potassium  dissolves  in  water,  there  remains  in  solu- 
tion a  compound  which,  on  electrolysis,  yields  sodium 
or  potassium  in  a  manner  exactly  parallel  to  the  forma- 
tion of  hydrogen  from  water. 

(In  the  following  paragraphs,  the  nature  of  caustic  potash 
alone  will  be  considered,  the  pupil  bearing  in  mind  that  what 
applies  to  that  substance  is  equally  true  of  caustic  soda.) 

Chemical  Structure  of  Caustic  Potash.  If  caustic  potash 
is  heated  with  potassium,*  hydrogen  will  soon  pass  off. 
If  the  hydrogen  developed  by  dissolving  a  weighed 
quantity  of  potassium  in  water  were  measured,  and 
the  resulting  volume  were  compared  with  that  obtained 
from  heating  the  same  weight  of  potassium  with  caustic 
potash,  the  two  quantities  would  be  found  to  be  iden- 
tical.14 The  action  of  potassium  on  water  can,  there- 
fore, be  divided  into  twflfetages,  —  first,  one-half  of  the 
hydrogen  contained  in  the  water  is  expelled, t  leaving 
caustic  potash  (potassium  hydroxide) ;  and  then  the 
second  half  can  be  removed  in  the  manner  mentioned 
above,  leaving  oxide-  of  potassium.^- 

*  In  a  silver  dish  or  glass  tube ;  hot  caustic  potash  attacks  a  platinum 
vessel,  while  the  clumsiness  and  weight  of  an  iron  one  are  objectionable. 

f  Provided  enough  potassium  is  used  to  change  the  entire  amount  of 
any  given  quantity  of  water  into  potassium  hydroxide. 

J  That  the  oxide  of  potassium  must  remain  will  be  seen  by  a  little 
reflection ;  for  water,  as  has  been  proven,  is  composed  of  hydrogen  and 
oxygen.  The  hydrogen  in  the  above  experiment  has  been  expelled  by 
potassium ;  but  as  no  oxygen  has  passed  off,  that  element  must  have 
remained  behind  in  combination  with  the  potassium.  That  the  oxide 
of  potassium  is  really  formed  in  this  way  can  be  provei£experimentally  by 
burning  a  little  piece  of  potassium  in  oxygen.  The  oxide  so  produced  is 
identical  with  that  formed  by  the  complete  action  of  potassium  on  water. 


PRODUCTS   OF  ACTION  OF  SODIUM,   ETC.         3l 

Formulation  of  the  Action  of  Potassium  on  Water.  In 
forming-  water,  two  volumes  of  hydrogen  unite  with  one 
volume  of  oxygen.  The  preceding  experiments  also 
show  that  the  hydrogen  in  water  can  be  divided  into 
two  parts.  These  two  facts  can  be  made  clearer  if 
we  represent  the  two  halves  of  hydrogen  obtained  from 
water  each  by  H,  and  the  oxygen  formed  by  the  same 
means  by  O.  The  structure  of  water  will  then  be 
represented  by  the  combination  HOH ;  and  designating 
the  potassium  which  acts  upon  water  by  a  letter  K,  the 
two  stages  of  the  reaction  could  be  represented  as  fol- 
lows :  — 

HOH  +  K  =  H  +  KOH. 
KOH  +  K  =  H  +  KOK.* 

The  potassium  in  potassium  oxide  is  therefore  com- 
posed of  two  halves,  just  as  much  as  is  the  hydrogen  in 
water,  so  that  caustic  potash  (potassium  hydroxide)  is 
simply  water  in  which  potassium  has  taken  the  place 
of  one-half  the  hydrogen,  while  rotassium  oxide  is  water 
in  which  potassium  has  replaced  all  of  the  hydrogen. 
Such  substitutions  are  by  no  means  uncommon  in  chem- 
ical reactions,  and  the  changes  studied  above  will  serve 
as  an  example  for  all  others. 

The  conclusion  at  which  we  have  arrived,  using  po- 
tassium, would  have  been  equally  apparent  had  we 
employed  sodium. 

*  In  these  equations  the  quantity  of  water  represented  by  HOH  is 
such  that  it  is  entirely  decomposed  by  the  amount  of  potassium  repre- 
sented by  K.  The  letter  K  is  used  to  designate  potassium,  because  it  is 
the  first  letter  of  the  Latin  name  (Kaliurri)  of  that  element. 


82  ELEMENTS   OF  CHEMISTRY. 


CHAPTER   VI. 

CHANGES   OF   ENERGY 

Which  take  place  in  the  Formation  of   Water,  Potassium 
Hydroxide,  and  Potassium  Oxide. 

Work  and  Energy.  Potential  Energy.  When  a  sub- 
stance, either  by  reason  of  its  position  or  of  its  motion, 
is  capable  of  performing  work,  it  is  said  to  possess 
energy.  When  energy  is  applied  to  overcoming  resist- 
ance, we  say  work  is  done.  The  energy  possessed  by  a 
body  may  be  divided  into  two  classes,  —  energy  of  posi- 
tion (potential  energy),  and  energy  of  motion  (kinetic 
energy).  A  stone  at  the  top  of  a  hill  possesses  poten- 
tial energy  ;  for,  by  reason  of  its  position,  it  is  capable 
of  performing  work  when  the  force  holding  it  in  place 
is  removed.  The  worK  which  it  can  do  is  measured  by 
the  mass  of  the  stone  multiplied  by  the  distance  through 
which  it  acts  (L  =  MS). 

Kinetic  Energy.  The  capacity  for.  work  which  a  body 
in  motion  possesses  by  reason  of  that  motion  is  called 
its  kinetic  energy;  and  the  measujje  of  this  is  one-half 
the  mass  of  the  body  multiplied  by  the  square  of  its 


.,     /Mv2 
velocity  (  - 


. 
* 


Conversion  of  Potential  into  Kinetic  Energy.     Conservation 
of  Energy.      If  a  portion  of  the   potential   energy  pos- 

*  For  the  derivation  of  this  formula,  consult  any  elementary  text-book 
on  physics. 


CHANGES   OF  ENERGY.  33 

sessed  by  a  body  is  converted  into  kinetic  energy  by  its 
assuming  motion,  then  the  snm  of  the  capacity  for  work 
still  remaining,  and  of  the  kinetic  energy  already  pro- 
duced, is  equal  to  the  potential  energy  originally  con- 
tained in  the  body.  This  sum  is  also  equal  to  the 
kinetic  energy  which  would  be  produced  if  its  entire 
potential  energy  had  been  used  for  the  performance  of 
work*  The  sum  of  the  potential  and  of  the  kinetic 
energy  is,  therefore,  constant.  (Principle  of  the  con- 
servation of  energy.) 

If  the  -  phenomena  attendant  upon  the  burning  of 
hydrogen  in  oxygen  are  recalled,  it  will  be  remembered 
that  heat  is  evolved  during  the  process.  If  this  heat 
were  properly  applied  (as,  for  instance,  in  changing 
water  into  steam  with  which  to  move  an  engine),  it 
would  be  capable  of  performing  work.*  Hydrogen  and 
oxygen,  when  in  contact,  possess  a  form  of  energy 
(chemical  energy)  which  is  akin  to  potential  energy. 
The  only  distinction  between  these  is  that  in  the  latter 
the  capacity  for  work  can  be  resolved  into  two  factors, 
the  weight  of  the  acting  body  and  the  distance  through 
which  it  acts,  while  in  the  former  the  distances 
through  which  the  action  takes  place,  and  the  weights 
of  the  particles  into  which  we  suppose  all  bodies  di- 
vided, are  so  small  that  chemical  energy  cannot  be 
resolved  into  two  factors.  The  amount  of  chemical 
energy  can,  however,  be  measured  by  the  amount  of 
work  which  given  weights  of  the  interacting  bodies  are 

*  This  tendency  which  certain  elements  have  to  unite  with  each  other 
to  form  compounds  is  termed  "chemical  affinity,"  or  "  chemism."  The 
nature  of  the  force  acting  between  the  elements  we  cannot  explain ;  hut 
it  is  by  reason  of  this  mutual  attraction  that  they  can  perform  work,  just 
as  tlve  stone  which  possesses  potential  energy  can  perform  work  owing 
to  the  attraction  of  gravitation. 


34  ELEMENTS  OP  CUEMIST&Y. 

capable  of  performing.  When  hydrogen  and  oxygen 
unite  to  form  water,  their  chemical  energy  is  converted 
into  kinetic  energy,  and  is  manifested  in  the  form  of 
heat  which  is  susceptible  of  measurement. 

i 

The  Energy  required  to  Decompose  a  Body  is  equal  to 
that  given  off  in  its  Formation.  A  stone  when  elevated 
above  the  ground  possesses  potential  energy.  When 
the  force  sustaining  this  stone  is  removed,  it  falls,  and 
in  so  doing  changes  its  potential  energy  into  kinetic 
energy.  To  raise  it  to  its  original  position  after  it  has 
fallen,  we  must  add  exactly  as  much  energy  as  was 
given  off  during  the  fall.  In  the  formation  and  decom- 
position of  water  we  are  confronted  by  a  parallel  case ; 
for  exactly  as  much  kinetic  energy  must  be  used  in  de- 
composing a  given  quantity  of  water  into  its  constituent 
elements,  oxygen  and  hydrogen,  as  was  given  off  in  the 
formation  of  the  same  weight  of  liquid.  We  accom- 
lished  the  decomposition  by  the  electric  current,  and 
the  quantity  of  electricity  used  could  perform  exactly 
as  much  work  as  could  the  heat  .given  off  in  forming 
the  water  which  was  decomposed.  This  conclusion  can 
be  summed  up  as  follows :  - 

The  kinetic  energy  given  off  in  the  formation  of  a 
given  weight  of  water  is  equal  to  the  kinetic  energy 
necessary  for  its  decomposition ;  or,  as  the  electricity 
used  in  the  breaking  down  can  be  converted  into  heat,* 


*  In  the  case  of  water  it  is  not  practically  possible  to  decompose  the 
compound  hy  heat  alone,  the  temperature  at  which  the  decomposition 
takes  place  being  too  high.  In  order  to  effect  the  decomposition  we 
must  resort  to  the  electric  current.  Heat  can,  however,  be  used  to  break 
down  many  other  compounds ;  and  in  such  cases  it  is,  of  course,  possible 
to  measure  the  heat  of  decomposition. 


CHANGES   OF  ENERGY.  35 

we  say  the  heat  of  formation  of  a  given  weight  of  water 
is  equal  to  the  heat  of  decomposition. 

Energy  Changes  in  forming  Sodium  and  Potassium  Hy- 
droxide. When  potassium  or  sodium  is  placed  in  contact 
with  water,  there  is  a  manifest  evolution  of  heat,  for 
the  metals  are  melted  as  they  float  on  the  surface.  In 
this  case,  however,  the  relationship  in  the  energy  is  not 
so  easily  understood  as  it  is  in  the  case  of  the  formation 
of  water,  because  a  portion  of  the  hydrogen  is  given  off 
from  the  water,  while  potassium  or  sodium  takes  its 
place.  To  form  potassium  hydroxide,  energy  must  first 
Be  added  to  the  water  in  order  to  decompose  that  sub- 
stance, and  so  expel  one-half  of  the  hydrogen.  It  is 
only  after  this,  that  potassium  can  take  its  place ;  but 
as  it  is  manifest  that  heat  is  given  off  during  the  com- 
plete change,  potassium  hydroxide  must  have  a  greater 
heat  of  formation  than  has  the  water  which  has  been 
decomposed  by  the  metal.  When  potassium  hydroxide 
has  once  been  formed,  it  is  in  the  same  condition  as  the 
stone  which  has  fallen  to  the  ground ;  i.e.,  energy  must 
be  added  to  bring  it  back  to  its  original  condition.  It 
follows  that  if  it  were  practically  possible  to  change 
potassium  hydroxide  back  into  water  and  potassium 
by  means  of  hydrogen,  the  hydrogen,  in  order  to  effect 
this  change,  would  have  to  be  assisted  by  an  amount 
of  kinetic  energy  equal  to  that  given  off  during  the 
decomposition  of  an  equivalent  quantity  of  water 
by  potassium. 

If  we  designate  a  given  quantity  of  hydrogen  by  X ,  an  amount 
of  oxygen  exactly  necessary  to  change  all  of  this  hydrogen  to 
water  by  F,  and  a  quantity  of  potassium  just  sufficient  to  decom- 


36  ELEMENTS   OF  CHEMISTRY. 

pose  the  water  so  formed  by  Z,  the  compounds  produced  being 
XY  (water),  —  YZ  (potassium  hydroxide)  then  :  — 

I.  II. 

X  +  Y  =  XY. 

Hydrogen  4-  Oxygen       =  Water. 

XY+Z          =|YZ  +  |. 

Water  +  Potassium  =  Potassium  hydroxide  +  Hydrogen.* 

In  each  case  the  substances  under  I.,  in  being  converted  into 
those  under  II.,  would  give  off  heat ;  they  consequently  possess 
energy,  for,  when  brought  in  contact,  they  are  capable  of  per- 
forming work. 

Energy  Changes  in  the  Formation  of  other  Compounds. 
Substances  which  mutually  possess  chemical  energy  are 
capable  of  entering  into  chemical  reactions  when  they 
are  brought  in  contact,  and  the  bodies  produced  by 
these  reactions  manifestly  possess  less  energy  than  the 
uncombined  constituents.  Thus  the  chemical  changes 
which  take  place  are  accompanied  by  an  evolution  of 
heat.  It  is,  however,  necessary  in  many  cases  to  give 
an  impulse  to  the  substances  which  we  intend  to  have 
enter  into  combination.  For  example,  we  saw  that 
hydrogen  and  oxygen  could  be  mixed  without  suffer- 
ing any  change,  the  chemical  union  of  the  two  gases 
taking  place  only  by  contact  with  a  flame  or  an  elec- 
tric spark.  This  condition  can  be  compared  to  that  of  a 
stone  at  the  brow  of  a  hill,  since  an  impulse  may  have 
to  be  given  it  before  it  begins  to  roll  toward  the  bottom. 

V 

*  In  these  equations  the  terms  XY  and  T^YZ  mean  hydrogen  and  oxy- 
gen joined  to  form  water,  and  oxygen,  potassium,  and  one-half  as  much 
hydrogen  united  to  form  potassium  hydroxide.  The  same  letters  sepa- 
rated by  the  sign -f- mean  that  the  substances  represented  are  mixed 
together,  but  that  they  have  not  as  yet  reacted  to  form  new  bodies.  The 
quantities  of  matter  to  the  left  and  to  the  right  of  the  sign  of  equality 
are  equal. 


CHANGES   OF  ENERGY.  37 

Kindling  Temperatures.  The  great  majority  of  bodies 
capable  of  uniting  with  oxygen,  and  of  evolving  light 
and  heat  during  the  change,  must,  as  is  the  case  with 
hydrogen,  first  be  heated  to  a  certain  degree  before  the 
union  begins  to  take  place.  The  temperature  at  which 
combination  with  oxygen  begins,  is  constant  for  a  given 
substance,  and  is  called  the  kindling  temperature  of  that 
substance,  while  the  subsequent  reaction  is  called  com- 
bustion. A  little  reflection  will  show  that  the  kindling 
temperature  of  different  bodies  may  vary  greatly ;  for  it 
is  a  matter  of  daily  experience  that  coal  has  a  very  high 
kindling  temperature,  while  phosphorus  *  can  be  ignited 
by  the  heat  produced  by  friction.15 

*  On  match-heads. 


38  ELEMENTS   OF  CHEMISTRY 


CHAPTER   VII. 

HYDROGEN   CHLORIDE. 

Common  Salt.  One  of  the  chemical  substances  most 
widely  distributed  is  common  salt.  It  is  fourtd  dis- 
solved in  sea-water,  in  the  water  of  rivers,  springs,  and 
lakes,  in  mineral  deposits  often  very  extensive  in  mass, 
and  in  animal  and  vegetable  tissues. 

Preparation  of  Hydrogen  Chloride.  If  salt  is  mixed 
with  sulphuric  acid,*  there  is  evolved  a  gas  with  a 
most  penetrating  and  acid  odor.  This  gas  is  called 
hydrogen  chloride.16 

Properties  of  Hydrogen  Chloride.  Hydrogen  chloride  is  a  color- 
less gas  at  ordinary  temperatures.  It  is  changed  to  a  liquid  at 
0°  under  a  pressure  of  twenty-six  atmospheres-!  It  is  extremely 
soluble  in  water,  one  cubic  centimetre  of  the  latter  absorbing  452 
cubic  centimetres  of  the  former  at  ordinary  temperatures.  The 
solution  has  a  specific  gravity  of  1.20,  and  contains  42  per  cent 
of  hydrogen  chloride.  "  Muriatic  "  or  "  hydrochloric  "  acid  is 
simply  this  solution  more  or  less  diluted  with  water.  Usually  it 
is  of  a  yellow  color,  owing  to  impurities ;  but  when  chemically 
pure,  it  is  colorless.  The  gas,  or  the  concentrated  solution,  appears 
to  smoke  (fume)  when  exposed  to  the  air,  a  phenomenon  due  to 
the  condensation  of  the  moisture  present  in  the  atmosphere  which 

*  See  page  56. 

t  The  question  of  changing  a  gas  to  a  liquid  is  merely  one  of  temper- 
ature and  pressure.  For  example,  steam  (gaseous  water)  is  changed  to 
a  liquid  (water)  at  100°,  and  at  the  pressure  of  one  atmosphere. 


HYDROGEN  CULOUIDE.  39 

forms  a  solution  of  hydrogen  chloride.  When  dissolving  in  water, 
hydrogen  chloride  causes  a  considerable  rise  in  the  temperature. 
A  volume  of  hydrogen  chloride  is  considerably  heavier  than  the 
same  volume  of  air,  its  specific  gravity  being  1.23  (air  =1).  In 
order  to  obtain  the  pure  gas,  it  must  be  collected  by  displacing 
dry  air  from  a  flask  placed  mouth  upward,  xor  by  expelling  mer- 
cury from  a  tube  filled  with  the  latter,  and  inverted  over  a  trough 
containing  the  same  substance.  Hydrogen  chloride  cannot  be 
collected  over  water,  owing  to  its  solubility  in  that  liquid.17 

The  Decomposition  of  Hydrogen  Chloride  by  Sodium.  In 
studying  the  chemistry  of  hydrogen  chloride,  the  first 
question  to  be  settled  is  whether  the  gas  is  a  compound 
or  an  element.  The  methods  which  suggest  themselves 
are,  naturally,  the  same  as  those  employed  for  the  de- 
composition of  water.  In  this  case,  however,  the  sodium 
or  potassium  cannot  be  treated  in  exactly  the  same 
way  as  in  the  investigation  of  the  chemical  structure  of 
water,  because  when  pieces  of  these  metals  are  brought 
in  contact  with  dry  hydrogen  chloride,  they  soon  be- 
come coated  with  the  solid  products  of  the  reaction  * 
which  ensues,  and  are  by  this  means  protected  from 
further  change.  We  can  avoid  this  interference  by  dis- 
solving sodium  or  potassium  in  mercury, f  and  then 
substituting  this  solution  for  the  pure  metals.  The 
changes  brought  about  will  not  be  altered  by  this  varia- 
tion in  the  conditions,  and  we  have  the  advantage  of 
avoiding  the  protective  coating. 

If  a  current  of  hydrogen  chloride  is  passed  through  a 
bottle  containing  sodium  amalgam,  the  gas  which  is  col- 


*  In  the  case  of  water  the  sodium  or  potassium  hydroxide  is  dissolved 
as  fast  as  it  is  formed,  and  the  metals  are,  therefore,  not  protected. 

f  The  solutions  produced  by  dissolving  metals  in  mercury  are  called 
amalgams.  The  solution  of  sodium  would  thus  he  called  sodium 
amalgam. 


40  ELEMENTS   OF  CHEMISTRY. 

lected  after  the  passage  is  no  longer  hydrogen  chloride. 
It  is  but  slightly  soluble  in  water,  it  has  no  odor,  and  it 
burns  in  the  air  with  a  colorless  flame  —  in  short,  it  is 
hydrogen.  We  have  already  seen  that  this  gas  is  not 
contained  in  the  sodium ;  the  only  possible  conclusion, 
therefore,  is  that  hydrogen  chloride  is  a  compound,  and 
that  it  contains  hydrogen.18 

Decomposition  of  Hydrochloric  Acid  by  the  Electric  Current.* 
What  are  the  other  constituents  of  hydrogen  chloride  ? 
The  answer  to  this  question  can  be  found  by  decom- 
posing hydrochloric  acid  by  the  electric  current  exactly 
as  was  done  with  water;  and  investigation  has  shown 
that  a  concentrated  solution  of  hydrochloric  acid  in  a 
saturated  t  solution  of  common  salt  is  the  best  sub- 
stance to  be  employed  in  order  to  study  this  change. 
If  two  pencils  of  gas  carbon  t  (connected  with  the  poles 
of  an  electric  battery)  are  placed  in  such  a  solution, 
bubbles  will  appear  first  at  the  negative  pole,  and  later 
at  the  positive  one.§  If  two  tubes  filled  with  the  liquid 
undergoing  decomposition  are  inverted  over  the  two 
pieces  of  carbon,  the  gases  produced  can  be  collected 
separately ;  and  if  the  tubes  are  of  the  same  size,  it  will 
be  seen  that  equal  volumes  of  the  two  gases  are  collected 
in  them  during  equal  intervals  of  time.  The  gas  forming 
at  the  negative  pole  is  easily  shown  to  be  hydrogen. 
That  at  the  positive  pole  has  a  peculiar  and  most  irri- 

*  The  solution  of  hydrogen  chloride  in  water  is  termed  hydrochloric 
acid. 

t  See  page  14. 

\  The  hard  pieces  of  carbon  used  in  producing  the  arc  electric  lights. 

§  The  reason  why  the  gas  does  not  appear  immediately  at  the  positive 
pole  is  hecause  it  is  to  a  certain  extent  soluble  in  the  liquid  undergoing 
decomposition.  Only  after  the  latter  has  taken  up  as  much  of  this  gas 
as  it  will,  does  the  excess  escape. 


* 


HYDROGEN   CFjLOmBE.     W         \ 

tating  odor  ;  it  bleaches  moist  vegetable  dyes  which  are 
brought  in  contact  with  it,  and,  owing  to  its  greenish- 
yellow  color,  is  called  chlorine.  Hydrogen  chloride  can, 
therefore,  be  decomposed  into  two  elements,  hydrogen 
and  chlorine.19 

Difference  between  the  Structure  of  Hydrogen  Chloride  and 
of  Water.  There  is  a  marked  difference  in  one  respect 
between  the  behavior  of  water  and  of  hydrogen  chloride 
toward  metals.  When  enough  sodium  or  potassium  acts 
on  the  former  to  insure  complete  decomposition,  the 
metal  liberates  but  one-half  of  the  hydrogen,  while  in 
the  case  of  the  latter  it  separates  the  entire  quantity. 
This  same  distinction  is  shown  by  the  relative  volumes 
of  the  gases  which  are  produced  by  electrolysis  ;  for 
water  is  decomposed  into  two  volumes  of  hydrogen  and 
one  of  oxygen,  while  hydrogen  chloride,  under  similar 
conditions,  yields  equal  amounts  of  hydrogen  and  of 
chlorine.  The  hydrogen  of  hydrogen  chloride  is  not, 
therefore,  separable  as  two  distinct  and  equal  portions 
like  that  of  water.  If,  then,  we  express  the  structure 
of  water  by  the  formula  HOH  (see  page  31),  we  can 
express  that  of  hydrogen  chloride  by  H  Cl. 

Formation  of  Hydrogen  Chloride  from  its  Constituent  Ele- 
ments. In  order  to  complete  all  of  the  data  necessary 
for  a  knowledge  of  its  structure,  it  only  remains  to 
prove  that  hydrogen  chloride  can  be  produced  from  hy- 
drogen and  chlorine.  This,  however,  is  not  so  easily 
accomplished  as  is  the  formation  of  water  from  hydro- 
gen and  oxygen,  because  of  the  practical  difficulty  that 
chlorine  cannot  be  collected  over  mercury  (see  page  24), 
as  it  readily  attacks  that  metal.  But  hydrogen  and 


42  ELEMENTS   OF  CHEMISTRY. 

chlorine  in  equal  volumes  (produced  by  the  decomposi- 
tion of  hydrogen  chloride  by  the  electric  current)  may 
be  passed  through  a  tube  with  a  glass  stopcock  at  each 
end  until  all  of  the  air  is  expelled.*  If  the  stop- 
cocks are  then  closed,  and  the  tube  is  left  in  diffused 
daylight,  the  hydrogen  and  chlorine  will  gradually 
unite,  and  the  gas  which  is  produced  will  have  exactly 
the  properties  which  characterize  hydrogen  chloride. 
If  care  is  taken  not  to  lose  any  of  the  product  of  the 
reaction,  we  can  easily  prove  that  the  volume  of  gas 
left  in  the  tube  after  the  union  has  taken  place  is 
exactly  equal  to  the  sum  of  the  volumes  of  hydrogen  and 
chlorine  with  which  it  was  filled  in  the  beginning. 
Hydrogen  chloride,  therefore,  is  produced  by  the  union 
of  equal  volumes  of  hydrogen  and  chlorine.™ 

The  volumes  of  hydrogen  and  chlorine  which  combine  to  form 
hydrogen  chloride  are  equal,  no  matter  how  the  acid  is  produced, 
and,  therefore,  hydrochloric  acid  is  formed  by  the  union  of  defi- 
nitely related  masses  of  its  constituent  elements.  As  a  given 
volume  of  hydrogen  always  has  a  constant  weight  when  meas- 
ured under  the  same  conditions,  and  as  this  is  necessarily  also 
true  of  a  given  volume  of  chlorine,  it  follows  that  hydrochloric 
acid  is  produced  by  the  interaction  of  definitely  related  weights 
of  hydrogen  and  chlorine.  As  the  volumes  of  these  two  gases 
when  they  enter  into  combination  are  equal,  it  must  be  true  that 
the  relative  weights  in  which  they  combine  are  to  each  other  in 
the  same  ratio  as  their  specific  gravities;  that  is,  as  1  to  35.45 
(see  page  27). 

Summary.  From  the  preceding  experiments  we  have 
learned  the  following  facts  :  — 

*  This  experiment  must  be  performed  in  a  dark  room,  A  mixture 
of  equal  volumes  of  hydrogen  and  chlorine  unite  with  a  sharp  explosion 
if  they  are  exposed  to  the  sunlight,  or  even  to  the  rays  of  an  arc  electric 
light,  or  to  those  of  a  burning  piece  of  magnesium. 


HYDROGEN  CHLORIDE.  43 

1.  Hydrogen  chloride  is  decomposable  into  hydrogen 
and  chlorine  by  means  of  the  electric  current. 

2.  Hydrogen  chloride    is  produced   from  hydrogen 
and  chlorine. 

3.  Equal  volumes  of  hydrogen  and  chlorine  unite  to 
form  .hydrogen  chloride,  and  the  gas  so  formed  occupies 
a  space  equal  to  the  sum  of  the  volumes  of  hydrogen 
and  chlorine  from  which  it  is  produced ;  or,  one  volume 
of   hydrogen   and   one   volume   of    chlorine    form  two 
volumes  of  hydrogen  chloride. 

4.  The  ratio  by  weight  in  which  hydrogen  and  chlo- 
rine unite  is  as  1:35.45. 

5.  Hydrogen  chloride  possesses  less  chemical  energy 
than  does  a  mixture  of  hydrogen  and  chlorine ;   for  if 
the  latter  mixture  is  brought  into  the  sunlight,  the  two 
gases  will  unite  with  a  sharp  explosion,  heat  and  light 
being  given  off  at  the  same  time. 

6.  Hydrogen   and   chlorine    possess    more    chemical 
energy  than  does  hydrogen  chloride.     The  latter  sub- 
stance is  extremely  stable,  but  can  be  broken  down  by 
the  electric  current,  or,  in  other  words,  by  the  addition 
of  energy  (see  page  34). 

Resemblances  between  Hydrogen  Chloride  and  Water.  All 
the  above  changes  are  exactly  parallel  to  the  similar 
ones  which  we  observed  while  studying  water ;  and  if 
we  measure  the  heat  given  off  in  the  formation  of  a 
given  weight  of  hydrogen  chloride,  and  the  heat-equiv- 
alent of  the  electricity  necessary  to  decompose  the  same, 
the  two  will  be  found  equal.  The  heat  of  decomposition 
of  hydrogen  chloride  is,  therefore,  equal  to  the  heat  of 
its  formation  (see  page  34).  When  hydrogen  chloride 
is  dissolved  in  water,  considerable  heat  is  evolved. 


44  ELEMENTS   OF  CHEMISTRY. 

Therefore,  the  solution  requires  more  energy  for  its 
decomposition  than  does  the  dry  gas.  In  consequence 
of  this  fact,  the  solution  is  of  necessity  more  stable. 
That  this  is  the  case  can  be  shown  by  the  follow- 
ing experiments  :  - 

If  a  mixture  of  hydrogen  chloride  and  oxygen  is  passed 
through  a  heated  tube,*  chlorine  is  developed,  while  water  is 
formed  by  the  union  of  the  hydrogen  of  the  chloride  with  the  free 
oxygen  which  has  been  added.  On  the  other  hand,  a  solution  of 
chlorine  in  water,  when  placed  in  direct  sunlight,  forms  hydro- 
chloric acid,  and  gives  off  oxygen.21  In  the  first  case,  then,  the 
hydrogen  chloride  and  oxygen  possess  more  energy  than  water 
and  chlorine.  In  the  second  case,  however,  the  water  being  de- 
composed by  the  chlorine,  this  relationship  is  exactly  reversed. 
Water  is,  therefore,  more  stable  than  is  dry  hydrogen  chloride, 
while,  on  the  other  hand,  hydrochloric  acid  in  solution  is  more 
stable  than  water.  The  bleaching  action  of  moist  chlorine 
(see  page  41)  can,  in  most  cases,  be  referred  to  the  effect  of 
oxygen  which  is  liberated  from  water,  the  oxygen  being  chemi- 
cally more  active  in  the  instant  of  its  separation  from  its  com- 
pound than  it  is  at  other  times.22 

*  The  tube  had  better  contain  porous  bodies,  such  as  pumice  stone. 


THE  ACTION   OF  METALS.  45 


CHAPTER   VIII. 

> 

THE   ACTION   OF   METALS 

On  Hydrochloric  Acid.     The  Neutralization  of  Hydrochloric 
Acid  by  Bases. 

WE  have  seen  that  when  sodium  acts  on  hydrogen 
chloride  a  change  is  produced  similar  to  the  one  which 
we  studied  when  considering  the  formation  of  sodium 
hydroxide  from  water,  with  the  difference  that,  in  the 
former  case,  if  enough  of  the  metal  is  added,  the  hydro- 
gen is  all  separated,  while  sodium  chloride  remains.  It 
is  a  matter  of  experience,  however,  that  more  metals 
will  spontaneously  react  with  hydrochloric  acid  than 
will  decompose  water. 

Action  of  Metals  on  Hydrochloric  Acid.  Pieces  of  zinc 
or  of  iron,*  when  placed  in  a  solution  of  hydrochloric 
icid,  are  instantly  attacked;  hydrogen  is  liberated, 
while  the  metals  dissolve.  If,  after  the  reaction 
is  completed,  the  excess  of  acid  is  evaporated,  there 
will  remain  behind  solid,  salt-like  bodies,  which  are 
chlorides  of  zinc  and  of  iron  respectively.23  The  paral- 
lelism between  these  changes  and  those  taking  place 
between  sodium  or  potassium  and  water  becomes  clear 
if  we  use  formulae  similar  to  those  already  employed 

*  The  metals  are  practically  not  acted  upon  by  water  at  ordinary 
temperatures.  The  solution  of  hydrogen  chloride  in  water  is  hydro- 
chloric acid. 


Just  as 


46  ELEMENTS   OF  CHEMISTRY. 

(on  page  31).  Representing  by  H  the  one  part*  of 
hydrogen  which  is  combined  with  the  35.45  parts  of 
chlorine  t  in  hydrochloric  acid,  and  the  corresponding 
chlorine  by  Cl,  we  have  — 

H  +  Cl  =  H  Cl. 

Hydrogen  +  Chlorine  =  Hydrochloric  acid,  and 

H  Cl  +  K  =  K  Cl  +  H. 

Hydrochloric  acid  +  Potassium  =  Potassium  chloride  +  Hydrogen. 

HOH  +  K  =  KOH  +  H. 

Water  +  Potassium  =  Potassium  hydroxide  +  Hydrogen. 

If  we  use  zinc  in  place  of  potassium,  representing 
by  zn  the  quantity  of  zinc  which  will  decompose  the 
above  weight  of  hydrochloric  acid  (i.e.,  which  contains 
one  part  of  hydrogen  combined  with  35.45  parts  of 
chlorine),  then  $  - 

zn  +  HCl  =  znCl  +  H.i 

Zinc  +  Hydrochloric  acid  =  Zinc  chloride  +  Hydrogen, 

or,  in  general,  using  the  term  Me  to  represent  any  metal 
which  is  acted  on  by  hydrochloric  acid  — 

Me  +  H  Cl  =  Me  Cl  +  ti. 

In  reacting  with  hydrochloric  acid,  the  metals,  while 
liberating  hydrogen,  form  the  corresponding  chlorides. 
The  chlorides  can,  therefore,  be  looked  upon  as  hydro- 

*  In  this  book  wherever  proportions  are  indicated  they  are  always 
understood  to  be  by  weight,  unless  volume  is  expressly  stated. 

t  Hydrogen,  as  we  have  seen,  combines  with  chlorine  in  the  ratio  of 
1 :  35.45.  If  we  select  35.45  as  the  weight  of  chlorine  in  the  above  exam- 
ples, we  have  numbers  which  may  be  called  combining  weights,  for  they 
represent  the  ratio  by  weight  in  which  hydrogen  and  chlorine  unite.  It 
is  obviously  of  advantage,  in  this  and  other  cases,  to  select  the  weight 
numbers  which  are  determined  for  us  by  nature. 

J  The  symbol  zn  is  used  to  designate  the  amount  of  zinc  which  will 
unite  with  as  much  chlorine  as  will  the  quantity  of  potassium  repre- 
sented by  the  symbol  K. 


THE  ACTION  OF  METALS.  47 

chloric  acid,  in  which  the  hydrogen  has  been  replaced 
by  other  metals. 

Changes  of  Energy  taking  place  during  the  Decomposition 
of  Hydrochloric  Acid  by  Metals.  Heat  is  developed  during 
the  decomposition  of  hydrochloric  acid  by  metals  so 
that  the  energy  changes  during  these  reactions  are  par- 
allel to  those  encountered  when  sodium  and  potassium 
are  brought  in  contact  with  water.  The  heat  given  off  in 
the  formation  of  the  metallic  chlorides  must,  therefore, 
exceed  that  required  for  the  decomposition  of  hydro- 
chloric acid.  Were  it  possible  to  convert  the  chloride 
back  to  the  metal  and  hydrochloric  acid  by  means  of 
hydrogen,  exactly  as  much  energy  would  have  to  be 
added  to  assist  this  reaction  as  was  given  off  in  the 
formation  of  the  chloride  from  the  metal  and  hydro- 
chloric acid. 

In  the  change  which  is  represented  by  the  equation  — 
H  Cl  +  Me  =  Me  Cl  +  H, 

the  substances  to  the  right  of  the  sign  of  equality  possess  less 
energy  than  do  those  to  the  left.  They  are  in  the  state  of  a  stone 
which  has  fallen  to  the  ground,  for  energy  must  be  added  to 
bring  them  back  to  their  original  condition.  The  reactions  men- 
tioned above  take  place  spontaneously,  because  chemical  energy 
can  be  transformed  into  kinetic  (see  page  35). 

Action  of  Hydrochloric  Acid  on  the  Oxides  of  the  Metals. 
The  chlorides  of  the  metals  can  be  formed  in  another 
and  much  more  general  way  than  by  the  direct  substi- 
tution of  hydrogen :  — 

EXAMPLE  :  —  If.  the  oxide  of  potassium  is  brought  in  contact 
with  hydrochloric  acid,  an  energetic  reaction  at  once  results, 


48  ELEMENTS   OF  CHEMISTRY. 

much  heat  is  developed,  and,  when  the  excess  of  liquid  is  evapo- 
rated, potassium  chloride  will  remain.  The  oxide  of  potassium  with 
hydrochloric  acid  produces  potassium  chloride  and  water. 

If  we  use  the  same  formula  for  oxide  of  potassium  that  wre 
used  on  page  31,  and  the  one  for  hydrochloric  acid  which  we 
employed  on  page  46,  then  the  change  can  be  represented  as 

follows :  — 

K  +  HC1      KC1      H* 

O  +0 

K  +  H  Cl      K  Cl      H 

What  is  true  of  potassium  oxide  is  true  of  most  of 
the  oxides  of  other  metals  as  well,  the  chlorides  being 
formed  by  the  action  of  these  oxides  on  hydrochloric 
acid.24 

Action  of  the  Hydroxides  of  the  Metals  on  Hydrochloric 
Acid.  If  we  compare  potassium  hydroxide  with  potas- 
sium oxide,  we  shall  see  that  the  former  can  be  looked 
upon  as  water  in  which  all  of  the  hydrogen  has  been 
replaced  by  potassium,  while  the  latter  is  water  in 
which  but  one-half  of  the  hydrogen  has  suffered  the 
same  substitution  (see  page  31).  It  seems  reasonable 
to  suppose,  therefore,  that  potassium  hydroxide,  being  of 
a  nature  similar  to  potassium  oxide,  will  react  similarly 
with  hydrochloric  acid,  and,  indeed,  this  is  the  fact. 

Potassium  hydroxide  with  hydrochloric  acid  also  produces  po- 
tassium chloride  and  water.  This  change  becomes  apparent  if 

*  In  order  to  secure  additional  clearness,  the  formula  for  potassium 
oxide  is  written  in  a  vertical  line.  This  obviously  makes  no  difference. 
It  thus  becomes  plain  that  the  hydrogen  of  the  hydrochloric  acid  unites 
with  the  oxygen  of  potassium  oxide  to  form  water.  The  quantity  of  hy- 
drochloric acid  represented  by  H  Cl  is  supposed  to  be  exactly  sufficient 
to  form  potassium  chloride  with  one-half  of  the  potassium  represented 
by  KOK.  We  must,  therefore,  use  twice  this  quantity  to  express  the 
complete  reaction.  It  is  also  clear  that  in  our  equation  the  hydrogen  of 
the  water  formed  is  divisible  into  two  halves  (see  page  31). 


THE  ACTION  OF  METALS.  49 

we  employ  formulae  similar  to  those  already  used  in  previous 

cases : — 

KOH  +  H  Cl  =  K  Cl  +  HOH.* 

What  is  true  of  potassium  hydroxide  is  also  true  of 
most  hydroxides  of  other  metals,  so  that  these  hydrox- 
ides, when  brought  in  contact  with  hydrochloric  acid, 
produce  the  corresponding  chlorides  and  water.  The 
oxides  and  hydroxides  of  metals  which  react  in  the 
above  manner  with  hydrochloric  acid  are  termed  bases.25 

Neutralization  of  Hydrochloric  Acid  by  Bases.  The 
changes  outlined  above  always  take  place  between  defi- 
nitely related  quantities  of  the  bases  and  of  hydrochloric 
acid. 

This  fact  can  readily  be  made  apparent  by  experiment,  but 
we  must  first  procure  some  means  of  discovering  with  certainty 
the  presence  of  a  base  when  it  is  dissolved  in  water.  This  means 
is  furnished  by  the  use  of  methyl  orange,  a  substance  prepared  in 
recent  years  by  a  complicated  chemical  process  from  one  of  the 
constituents  of  coal-tar.  A  solution  of  methyl  orange  in  water  is 
of  an  orange  color  when  a  soluble  base  is  present,  but  turns  to 
deep  red  on  contact  with  an  acid.t  26 

If  a  weighed  quantity  of  potassium  hydroxide  is  dis- 
solved in  water,  a  very  little  methyl  orange  added,  and 
then  hydrochloric  acid  is  carefully  run  into  the  solution 
drop  by  drop,  a  point  will  finally  be  reached  at  which 

*  The  quantity  of  hydrochloric  acid  here  selected  and  represented  by 
H  Cl  is  supposed  to  be  exactly  enough  to  form  potassium  chloride  with 
the  potassium  present  in  the  hydroxide  used.  Experience  teaches  us 
that  the  amount  of  hydrogen  in  the  acid  will  be  exactly  enough  to  form 
water  with  the  oxygen  and  hydrogen  present  in  potassium  hydroxide. 

t  Substances  which  turn  the  red  solution  of  methyl  orange  to  orange 
yellow  are  called  alkaline.  The  orange  solution  is  said  to  be  of  an 
"  alkaline  reaction,"  and  the  substance  (in  this  case  methyl  orange) 
which  shows  that  the  alkali  is  present  is  termed  an  "indicator."  Sub- 
stances which  have  the  opposite  effect  are  said  to  be  of  an  "  acid 
reaction." 


50  ELEMENTS   OF  CHEMISTRY. 

the  orange  yellow  of  the  "  indicator  "  changes  to  red. 
A  trace  of  potassium  hydroxide  would  now  restore  the 
original  color,  which,  again,  a  trace  of  acid  would  alter 
to  red.  At  this  point  the  liquid  is  said  to  be  neutral. 
If  the  excess  of  water  is  evaporated  from  this  solution, 
nothing  but  potassium  chloride  remains  ;  for  all  the 
caustic  potash  and  all  the  hydrochloric  acid  have  re- 
acted with  each  other  to  form  the  salt. 

We  have  supposed  that  we  started  with  a  definite  quantity  of 
potassium  hydroxide.  Let  us  suppose  also  that  the  solution 
of  hydrochloric  acid  is  so  prepared  that  we  know  exactly  the 
amount  of  that  substance  in  a,  cubic  centimetre  of  liquid.  It  is 
then  obvious  that,  by  measuring  the  number  of  cubic  centimetres 
which  it  takes  to  neutralize  the  base,  we  can  ascertain  the  total 
amount  of  acid  which  is  used  for  such  neutralization.  Repeated 
experiments  will  show  that,  with  a  fixed  quantity  of  potassium 
hydroxide,  the  amount  of  acid  necessary  for  neutralization  is  also 
fixed,  no  matter  what  circumstances  may  surround  the  experi- 
ments. What  is  true  of  potassium  hydroxide  is  true  of  all  other 
bases,  so  that  — 

A  fixed  quantity  of  hydrochloric  acid  is  always  neu- 
tralized by  an  unvarying  quantity  of  a  given  base,  but 
the  amounts  which  will  neutralize  this  quantity  are 
never  alike  with  different  bases.27 

FOR  EXAMPLE  :  —  One  part  of  hydrochloric  acid  is  always 
exactly  neutralized  by 

1.535  parts  of  potassium  hydroxide, 
1.096  parts  of  sodium  hydroxide, 
1.014  parts  of  calcium  hydroxide, 
0.791  parts  of  magnesium  hydroxide, 
1.360  parts  of  zinc  hydroxide,  etc. 

We  shall  subsequently  see  that  what  is  true  of  hy- 
drochloric acid  is  true  of  all  other  acids  as  well ;  i.e., 


THE  ACTION  OF  METALS.  51 

the  salts  are  formed  by  the  interaction  of  quantities  of 
acids  and  bases  which  bear  a  definite  relationship  to  each 
other  by  weight.  These  facts  are  not  unexpected  if 
we  consider  that  every  one  of  the  chemical  compounds 
heretofore  encountered  is  formed  by  the  union  of  defi- 
nitely related  masses  of  the  elements. 

Energy  Changes  during  the  Neutralization  of  Bases  by 
Hydrochloric  Acid.  During  the  neutralization  of  bases 
by  hydrochloric  acid,  heat  is  given  off,  so  that  the  chlo- 
ride and  the  water  which  are  formed  possess  less  energy 
than  do  the  hydroxide  and  the  acid.  The  substances 
to  the  right  of  the  sign  of  equality  in  the  following 
equation,  therefore  (as  in  the  previous  cases  which  have 
been  cited),  possess  less  energy  than  those  to  the  left; 
for  work  must  be  done  (energy  added)  to  bring  them 
back  to  their  original  condition  :  - 

Me  OH  +  H  01  =  Me  Cl  +  HOH. 

Base  (metallic  hydroxide)  +  Hydrochloric  acid  =  Metallic  chloride  +  Water. 

Summary.  The  facts  which  have  been  brought  for- 
ward in  the  last  chapter  can  be  summed  up  as 
follows :  - 

1.  Hydrochloric  acid  attacks  many  metals,  hydrogen 
being  liberated,  and  the  chloride  remaining. 

2.  Heat  is  given  off  daring  the  changes,  consequently 
the  chlorides  possess  less  energy  than  the  metals  and 
the  acid. 

3.  Hydrochloric  acid  unites  with  the  oxides  of  met- 
als (bases)  to  produce  the  chlorides  and  water.     This 
change  is  termed  the  neutralization  of  the  base  by  the 
acid. 

4.  Hydrochloric  acid  reacts  with  the  hydroxides  of 


52  ELEMENTS   OF  CHEMISTRY. 

metals  .(bases)   to    produce    the    chlorides    and  water. 
This  is  also  termed  neutralization. 

5.  The  replacement  (substitution)  of  the  hydrogen 
in  the  acid  takes  place  in  such  a  way  that  a  fixed  quan- 
tity of  a  given  metal  always  takes  the  place  of  a  fixed 
quantity  of  hydrogen.     There  is  a  definite  relationship, 
therefore,  between  the  mass  of  the  metal  dissolved,  the 
mass  of  hydrogen  evolved,  and  the  mass   of  chlorine 
found  united  to  the  metal  in  the  chloride.     This  rela- 
tionship is  constant  for  any  one  metal,  but  is  different 
for  any  two  metals. 

6.  The  neutralization  of  the  acid  always  takes  place 
in  such  a  way  that  there  is  a  definite  ratio  between  the 
mass  of  the  base  neutralized  and  the  mass  of  the  acid 
used  for  neutralization.      The  chloride  produced  also 
contains  the  same  proportion  of  metal  to  chlorine  as  it 
would  contain  were  it  formed  by  dissolving  the  metal 
in  the  acid. 

7.  Heat  is  given  off  during  the  processes  of  neutrali- 
zation, consequently  the  chloride  and  the  water  which 
are  formed  possess  less  energy  than  the  base  and  the 
acid  before  neutralization. 


THE    OXIDES    OF   SULPHUR.  53 


CHAPTER   IX.    . 

THE   OXIDES   OF  SULPHUR. 

The  Chief  Oxides  of  Sulphur,  and  the  Acids  derived  from  these 
Oxides.  The  Laws  of  Definite  and  Multiple  Proportions.  The 
Neutralization  of  Sulphuric  Acid  by 


Acids  and  Salts  in  General.  The  processes  of  neutrali- 
zation with  which  we  became  familiar  during  the  study 
of  hydrochloric  acid  are  of  fundamental  importance  in 
chemistry,  because  there  is  a  vast  number  of  other  acids 
which,  like  hydrochloric,  react  with  bases.  Hydrogen 
chloride  contains  only  two  elements,  but  most  acids  are 
formed  from  three  or  even  more.  In  any  event,  one  of 
these  elements  must  be  hydrogen,  which  is  replaceable 
by  other  metals.  The  term  salt  is  applied  to  substances 
produced  either  by  direct  substitution  of  the  acid  hydro- 
gen by  metals,  or  by  neutralization  of  bases ;  and  a  given 
salt  has  the  same  composition,  no  matter  what  the  man- 
ner of  its  formation  may  be. 

Undoubtedly  the  most  important  of  acids  is  sulphuric 
acid ;  and,  in  order  to  understand  the  nature  of  this  sub- 
stance, it  is  necessary  to  inquire  into  the  manner  of  its 
formation.  This  we  can  most  successfully  do  by  first 
studying  the  product  formed  by  burning  sulphur  in 
oxygen. 

Formation  of  Sulphur  Dioxide.  If  sulphur  is  ignited,  it 
burns  with  a  blue  flame,  the  sulphur  disappears,  and  a 
gas  takes  its  place.  If  the  combustion  is  performed  in 


54  ELEMENTS   OF  CHEMISTRY. 

a  jar  of  pure  oxygen  with  a  sufficient  quantity  of  sul- 
phur, nothing  but  this  gas  (sulphur  dioxide)  will  re- 
main, and  the  volume  of  sulphur  dioxide  produced  is  the 
same  as  the  volume  of  oxygen  entering  into  its  formation.*® 

Formation  of  Sulphur  Trioxide  from  Sulphur  Dioxide.  A 
large  amount  of  heat  is  given  off  when  sulphur  burns, 
so  that  the  sulphur  dioxide  which  is  produced  by  this 
process  obviously  possesses  much  less  energy  than  do 
the  oxygen  and  sulphur  from  which  it  is  formed.  Sul- 
phur dioxide  is,  however,  capable  of  still  further  union 
with  oxygen  if  placed  under  proper  conditions,  and  the 
product  of  this  union  is  a  solid  called  sulphur  trioxide?® 

The  quantities  of  oxygen  which  are  united  with  a  fixed 
amount  of  sulphur  in  the  above  two  oxides  are  to  each  other  in 
the  ratio  of  2  to  3 ;  for  in  sulphur  dioxide  one  part  by  weight  of 
sulphur  is  united  to  one  of  oxygen,  while  in  sulphur  trioxide  one 
part  of  sulphur  is  combined  with  one  and  one-half  parts  of 
oxygen.* 

These  facts  can  be  summed  up  as  follows :  — 

1.  Each  of  the  oxides  of  sulphur  is  produced  by  the 
union  of    definitely  related  weights  of   sulphur  and   of 
oxygen. 

2.  The  weight  of  oxygen  which  is  united  to  a  fixed 
amount  of  sulphur  in  sulphur  dioxide  is  in  simple  ratio 
,to  the  weight  of  oxygen  which  is  united  to  the  same 
fixed  quantity  of  sulphur  in  sulphur  trioxide. 

The  statement  made  in  the  first  of  the  above  clauses 
is  equally  true,  as  we  have  seen,  if  rt  is  applied  to  any 
one  of  the  chemical  compounds  which  we  have  studied ; 

*  Sulphur  dioxide,  when  wanted  for  laboratory  use,  is  not  prepared 
by  the  burning  of  sulphur.  The  method  which  is  employed,  and  the 
means  of  converting  sulphur  dioxide  into  sulphur  trioxide,  are  given  in 
the  Laboratory  Appendix,  experiments  28  and  29. 


THE   OXIDES    OF  SULPHUR.  55 

that  in  the  second  will  be  found  to  apply  to  every  series 
of  compounds  in  which  each  member  is  produced  by  the 
union  of  the  same  two  elements.  Facts  so  general  in 
their  application  as  these  can  be  summed  up  in  the  form 
of  laws,  so  that  as  the  basis  of  chemical  science  we  have 
the  result  of  extended  investigation  in  the  following :  - 

1.  Law  of  Definite  Proportions.     Every  chemical   com- 
pound contains  its  constituent  elements  in  an  unvarying 
ratio  by  weight,  no  matter  under  what  circumstances  the 
compound  may  be  formed. 

2.  Law  of  Multiple  Proportions.     If  two   elements   (A 
and  B)  unite  in  more  than  one  proportion,  the  parts  of 
B  which  enter  into  combination  with  a  fixed  quantity  of 
A  will,  in  the  series  so  produced,  be  in  simple  ratio  to 
each  other. 

EXAMPLES  OF  LAW  1. 

One  part  of  hydrogen  always  unites  with  8  parts  of 
oxygen  to  produce  water. 

One  part  of  hydrogen  always  unites  with  35.5  parts 
of  chlorine  to  produce  hydrogen  chloride. 

One  part  of  hydrogen  always  unites  with  39  parts 
of  potassium  and  16  parts  of  oxygen  to  produce  potas- 
sium hydroxide; 

EXAMPLES  OF  LAW  2. 

Sulphur  and  oxygen  produce  two  compounds.  In 
one  of  these  one  part  of  sulphur  unites  with  one  part  of 
oxygen  to'  produce  sulphur  dioxide ;  in  the  other,  one 
part  of  sulphur  unites  with  one  and  one-half  parts 
of  oxygen  to  produce  sulphur  trioxide.  Proportions 
of  oxygen,  2:  3.  ^»  THl^ 

HJIIViaSXTT] 

-**»      *.  .  /I 


56  ELEMENTS   OF  CHEMISTRY. 

Iron  and  sulphur  produce  two  compounds.  In  one 
of  these  one  part  of  iron  unites  with  1.143  parts  of 
sulphur ;  in  the  other,  one  part  of  iron  unites  with  2.286 
parts  of  sulphur.  Proportions  of  sulphur,  1:2. 

Nitrogen  and  oxygen  produce  five  compounds.  In 
this  series  one  part  of  nitrogen  is  united  with  .569, 
1.138,  1.707,  2.276,  and  2.845  parts  of  oxygen.  Pro- 
portions, 1:2:3:4:5. 

Properties  of  Sulphur  Trioxide.  Sulphur  trioxide  is  a  colorless 
liquid  at  ordinary  temperatures.  Below  15°  it  changes  to  a  solid. 
It  boils  at  46°,  and  forms  a  colorless  vapor  having  a  specific  grav- 
ity of  2.76.  (Air  =  1.) 

Formation  of  Sulphuric  Acid  from  Sulphur  Trioxide.  Sul- 
phur trioxide  dissolves  in  water  with  a  hissing  noise, 
resembling  that  attending  the  immersion  of  a  red-hot 
iron;  much  heat  is  developed,  and  if  the  excess  of 
liquid  is  evaporated  there  remains  an  oil-like  fluid 
which  is  termed  sulphuric  acid.30  Sulphuric  acid  is, 
therefore,  formed  by  the  union  of  water  with  sulphur 
trioxide  (which  is  termed  an  anhydride). 

The  Anhydrides  of  Acids.  The  anhydrides  of  acids 
constitute  a  class  of  bodies  which  has  many  representa- 
tives. They  are  oxides  of  not-metals  which  on  addi- 
tion of  water  unite  with  that  substance  to  produce  the 
corresponding  acids. 

EXAMPLES  :  —  Sulphuric  anhydride  (sulphuric  trioxide)  by  the 
addition  of  water  produces  sulphuric  acid. 

Phosphoric  anhydride  (produced  by  burning  phosphorus  in 
oxygen)  by  the  addition  of  water  produces  phosphoric  acid. 

Nitric  anhydride  (a  compound  of  nitrogen  and  oxygen)  by 
the  addition  of  water  produces  nitric  acid. 


THE  OXIDES   OF  SULPHUR.  57 

Properties  of  Sulphuric  Acid.  Sulphuric  acid  is  a  colorless 
liquid  which  on  superficial  examination  appears  like  an  oil. 
When  pure  it  has  a  specific  gravity  of  1.88  (water  =  1) ;  at  0°  it 
crystallizes  in  large  prisms  which  melt  at  10°.5.  It  boils  at  338°; 
but  before  that  point  is  reached  the  acid  begins  to  decompose 
into  sulphur  trioxide  and  water,  or,  in  other  words,  in  a  direction 
which  is  the  reverse  of  that  of  its  formation.  This  separation  is 
complete  at  a  temperature  somewhat  above  the  boiling-point  of 
the  acid.  Sulphuric  acid  has  a  strong  inclination  to  take  up  water. 
During  the  process  of  solution  a  great  amount  of  heat  is  devel- 
oped; the  diluted  acid,*  therefore,  possesses  much  less  energy 
than  does  the  pure,  and,  as  a  consequence,  it  is  less  readily  decom- 
posed. Concentrated  sulphuric  acid  violently  attacks  the  skin 
and  mucous  membrane,  so  that  it  is  a  poison.31 

Action  of  Metals  on  Diluted  Sulphuric  Acid.  It  is  obvi- 
ous that  sulphuric  acid  must  contain  hydrogen,  for 
it  is  produced  by  the  union  of  sulphur  trioxide  with 
water.  That  this  hydrogen  can  be  replaced  by  other 
metals  is  proven  by  the  following  experiments  :  - 

When  diluted  sulphuric  acid  is  brought  in  contact 
with  pieces  of  zinc,  a  gas  is  developed  which  can  easily 
be  identified  as  hydrogen.  If  the  excess  of  liquid  is 
evaporated  (after  as  much  zinc  has  been  added  as  the 
acid  will  dissolve),  a  solid  crystalline  substance  (zinc 
sulphate)  will  remain.  Similar  phenomena  are  observed 
when  iron  or  magnesium  is  added  to  dilute  sulphuric 
acid.  With  the  former  iron  sulphate  is  formed,  while 
with  the  latter  magnesium  sulphate  is  produced.  So- 
dium or  potassium  also  reacts  with  diluted  sulphuric 
acid  with  the  greatest  violence,  hydrogen  being  evolved, 
while  sodium  or  potassium  sulphate  remains  after  evap- 

*  Dilute  slowly  by  adding  sulphuric  acid  to  an  excess  of  water,  not  by 
adding  water  to  sulphuric  acid;  otherwise,  the  heat  produced  may  be 
great  enough  to  cause  the  water  to  boil,  and  in  this  way  drops  of  hot  acid 
may  be  scattered  about. 


58  ELEMENTS   OF  CHEMISTRY. 

oration.  Zinc  sulphate,  iron  sulphate,  magnesium  sul- 
phate, sodium  sulphate,  and  potassium  sulphate  are 
salts ;  for,  as  we  have  seen,  they  are  produced  by  re- 
placing the  hydrogen  of  sulphuric  acid  by  other  metals.32 

Neutralization  of  Sulphuric  Acid  by  Bases.  The  phe- 
nomena which  have  just  been  detailed  are  parallel  to 
those  which  we  observed  while  studying  hydrochloric 
acid  (see  page  46  and  following)  ;  and  in  order  to  make 
this  parallelism  more  apparent,  the  processes  attending 
the  neutralization  of  sulphuric  acid  should  next  be  con- 
sidered. 

The  oxides  of  zinc,  iron  (ferrous  oxide),  or  magne- 
ium,  are  insoluble  in  water ;  but  they  readily  dissolve 
in  djluted  sulphuric  acid.  If  in  each  case  enough  of 
the  oxide  is  added  to  the  acid  so  that  a  portion  will 
remain  undissolved  (even  after  standing  for  some 
time),  and  if  then  this  excess  is  removed  by  nitration, 
sulphates,  identical  with  those  obtained  by  ,the  action 
of  diluted  sulphuric  acid  on  the  corresponding  metals, 
will  be  deposited  as  crystalline  solids  upon  evaporating 
the  excess 'of  the  liquid.  In  the  same  way  sodium 
oxide  will  produce  sodium  sulphate,  and  potassium 
oxide,  potassium  sulphate.  Sulphuric  acid  is,  therefore, 
neutralized  by  these  oxides  to  form  the  corresponding 
salts  and  water,  and  similar  processes  can  also  be  ob- 
served upon  the  solution  in  sulphuric  acid  of  a  very 
large  number  of  the  oxides  of  other  metals.33 

Difference  between  the  Neutralization  of  Sulphuric  Acid 
and  of  Hydrochloric  Acid.  So  far  we  have  observed  no 
distinction  between  the  action  of  sulphuric  acid  and 
hydrochloric  acid  during  the  process  of  neutralization. 


THE  OXIDES   OF  SULPHUR.  59 

That  there  is  a  marked  difference,  however,  will  become 
apparent  as  soon  as  we  study  the  neutralization  of  sul- 
phuric acid  by  means  of  sodium  or  potassium  hydroxide. 
We  weigh  off  sodium  hydroxide  and  sulphuric  acid  in 
such  proportions,  that  for  one  part  of  the  former  we 
have  2.45  parts  of  the  latter,  and  then,  after  dissolving 
the  sodium  hydroxide  in  water  and  diluting  the  sul- 
phuric acid  with  the  same,  bring  the  two  solutions  in 
contact.  All  the  sulphuric  acid  and  all  the  sodium 
hydroxide  will  enter  into  the  reaction,  and  a  salt  will 
be  produced.  This  salt  can  be  isolated  by  evaporating 
the  excess  of  liquid.  It  differs  from  those  we  have 
previously  encountered  in  the  fact  that,  in  spite  of  its 
being  formed  by  the  action  of  an  acid  on  a  base,  it  still 
contains  replaceable  hydrogen.*  This  salt,  therefore, 
has  resulted  from  replacing  by  sodium  only  a  portion 
of  the  available  hydrogen  of  sulphuric  acid.  That  this 
is  a  fact  can  readily  be  shown  by  dissolving  the  salt  in 
water,  adding  a  second  quantity  of  sodium  hydroxide 
equal  to  the  first,  and  again  evaporating  the  excess  of 
liquid.  There  will  remain  a  sodium  sulphate,  which 
no  longer  contains  replaceable  hydrogen ;  and  this  sub- 
stance differs  radically  in  properties  from  the  one  which 
was  isolated  in  the  first  instance.  The  salts  which  are 
produced  by  replacing  only  one-half  the  hydrogen  of 
sulphuric  acid  by  metals  are  termed  primary  or  acid ; 
those  formed  by  replacing  all  the  hydrogen,  secondary 
or  neutral  sulphates.3* 

Comparison  of  the  Structure  of  Sulphuric  Acid  and  of 
Water.  In  its  structure  sulphuric  acid  can  be  com- 
pared to  water;  for  its  hydrogen  is  divisible  into  two 

*  I.e.,  hydrogen  which  can  be  replaced  by  other  metals  to  form  a  salt. 


60  ELEMENTS   OF  CHEMISTRY. 

halves  by  means  of  metals,  just  as  the  hydrogen  of 
water  is.  This  parallelism  will  be  made  clear  if  we 
consider  the  following  two  formulae  (X  representing 
what  is  united  with  hydrogen  to  form  sulphuric 
acid) :  - 

H  -  O  -  H         and         H  -  X  -  H 

Water.  Sulphuric  acid. 

The  substitution  of  hydrogen  by  sodium  in  these  two 
substances  can  be  expressed  as  follows :  — 

1.  Na  *  +  HOH  =  Na  OH         +  H. 

Sodium  +  Water  =  Sodium  hydroxide  +  Hydrogen. 

Na  OH  +  Na  =  Na  ONa  +  H. 

Sodium  hydroxide  +  Sodium  =  Sodium  oxide  +  Hydrogen. 

2.  Na    +    HXH      =  Na  XH  +  H. 

Sodium  +  Sulphuric  acid  =  Primary  sodium  sulphate  +  Hydrogen. 

Na  XH  +  Na   =  Na  X  Na  +  H. 

Primary  sodium  sulphate  +  Sodium  =  Secondary  sodium  sulphate  +  Hydrogen. 

Comparison  of  the  Structure  of  Hydrochloric  Acid  with  that 
of  Sulphuric  Acid.  When  sodium  hydroxide  is  brought 
in  contact  with  twice  as  much  hydrochloric  acid  as  it  is 
capable  of  neutralizing,  one-half  the  available  hydro- 
gen will  be  replaced  by  the  sodium ;  but  this  hydrogen 
will  be  the  constituent  part  of  only  one-half  the  hydro- 
chloric acid,  while  the  other  half  will  remain  unchanged. 
With  sulphuric  acid,  on  the  other  hand,  if  the  same 
quantitative  relationship  between  the  base  and  the  acid 
is  retained,!  one-half  the  hydrogen  will  also  be  replaced ; 
but,  at  the  same  time,  all  the  sulphuric  acid  will  have 

*  The  quantity  of  sodium  represented  by  the  symbol  Na  is,  as  in  pre- 
vious instances,  supposed  to  be  exactly  enough  to  substitute  one  part  by 
weight  of  hydrogen. 

f  I.e.,  if  one-half  as  much  sodium  hydroxide  as  is  necessary  for  com- 
plete neutralization  of  the  sulphuric  acid  is  added. 


THE  OXIDES   OF  SULPHUR.  61 

entered  into  the  reaction  and  so  have  produced  the 
primary  sulphate  of  sodium.  An  acid  like  hydrochloric 
acid  is  termed  a  monobasic  acid ;  an  acid  like  sulphuric 
acid  is  termed  a  dibasic  acid.  What  is  true  of  hydro- 
chloric acid  and  of  sulphuric  acid  is  equally  true  of  all 
monobasic  and  diabasic  acids. 

The  Sulphates  are  formed  by  the  Interaction  of  Definitely 
Related  Weights  of  Bases  and  of  Sulphuric  Acid.  The 
method  by  which  we  can  ascertain  that  an  unvarying 
amount  of  a  given  base  is  always  necessary  to  neutral- 
ize completely  a  fixed  quantity  of  sulphuric  acid  is  iden- 
tical with  that  employed  in  the  study  of  hydrochloric 
acid  (see  page  49).  A  little  methyl  orange  (page 
49)  is  added  to  dilute  sulphuric  acid,  and  then  potas- 
sium hydroxide  or  sodium  hydroxide  solution  is  added 
until  the  color  just  changes  from  deep  red  to  orange 
yellow.  At  this  point  the  sulphuric  acid  will  be  com- 
pletely neutralized,  and  the  secondary  sulphate  will  be 
formed.  If  we  start  with  a  definite  quantity  of  the 
base,  and  if  the  solution  of  sulphuric  acid  is  so  pre- 
pared that  we  know  exactly  the  amount  of  that  sub- 
stance in  a  cubic  centimetre  of  the  liquid,  it  is  obvious 
that,  by  measuring  'the  number  of  cubic  centimetres 
which  it  takes  to  neutralize  the  base,  we  can  ascertain 
the  total  amount  of  the  acid  used  for  such  neutrali- 
zation. If  this  method  is  carefully  followed  out,  a 
series  of  experiments  will  develop  the  following 
law.35 

A  fixed  quantity  of  sulphuric  acid  is  always  com- 
pletely neutralized  by  an  unvarying  quantity  of  a  given 
base,  but  in  no  two  different  bases  are  the  amounts  which 
will  neutralize  this  quantity  of  acid  alike. 


62  ELEMENTS   OF  CHEMISTRY. 

EXAMPLES  :  —  One  part  by  weight  of  sulphuric  acid  is  always 
completely  neutralized  by  — 

1.143  parts  by  weight  of  potassium  hydroxide, 
0.817  parts  by  weight  of  sodium  hydroxide, 
0.755  parts  by  weight  of  calcium  hydroxide, 
0.595  parts  by  weight  of  magnesium  hydroxide, 
1.013  parts  by  wreight  of  zinc  hydroxide,  etc. 

If  we  compare  the  above  table  with  the  similar  one 
on  page  50,  in  which  the  quantities  of  the  same  hy- 
droxides necessary  to  neutralize  one  part  of  hydrochlo- 
ric acid  are  given,  there  will  be  brought  to  light  the 
remarkable  fact  that  the  amounts  of  the  hydroxides  are 
in  the  same  ratio.  This  fact  will  become  apparent  if 
we  multiply  all  of  the  numbers  in  the  first  table  by 
86.5,  and  all  of  those  in  the  second  by  49 ;  *  for 

56       parts  of  potassium  hydroxide, 
40       parts  of  sodium  hydroxide, 
39       parts  of  calcium  hydroxide, 
29.5    parts  of  magnesium  hydroxide, 
49.65  parts  of  zinc  hydroxide, 

are  completely  neutralized  either  by  36.5  parts  of  hydro- 
chloric acid,  or  by  49  parts  of  sulphuric  acid.  If  simi- 
lar investigations  are  conducted  with  any  other  acid, 
the  above  parts  of  the  hydroxides  are  also  the  quanti- 
ties which  are  necessary  to  neutralize  that  particular 
amount  of  any  acid  which  contains  one  part  of  hydro- 
gen ;  and  from  this  it  follows  that  the  reverse  must  also 
be  true.  We  could,  therefore,  construct  a  table  of 
acids  with  numbers  so  selected  that  each  would  repre- 

*  The  reason  for  selecting  36.5  and  49  as  the  numbers  with  which  to 
multiply  the  quantities  is  that  36.5  and  49  are  the  parts  by  weight  of 
hydrochloric  acid  and  of  sulphuric  acid  which  contain  one  part  by  weight 
of  hydrogen. 


THE  OXIDES   OF  SULPHUR.  68 

sent  a  weight  of  acid  containing  one  part  of  hydrogen, 
and  then  any  one  of  those  quantities  would  exactly 
neutralize  any  one  of  the  amounts  given  in  the  above 
table  of  hydroxides.  It  is,  of  course,  understood  that 
all  these  weights  are  to  be  measured  by  the  same  unit. 
The  relative  weights  of  bases  and  acids  so  ascertained 
are  termed  their  equivalent  weights. 

Relationship  between  the  Amounts  of  Base  Necessary  to 
form  the  Primary  and  Secondary  Sulphates.  It  has  been 
shown  that  the  hydrogen  of  sulphuric  acid  is,  like  that 
of  water,  divisible  into  two  equal  parts  by  the  action 
of  sodium  or  potassium  hydroxide.  We  should  there- 
fore select,  as  a  basis  for  consideration,  not  the  equiva- 
lent weight  of  sulphuric  acid,  but  twice  that  amount, 
or,  in  other  words,  that  part  by  weight  of  sulphuric 
acid  which  contains  two  parts  of  hydrogen.  If  we  do 
this,  we  find  that  98  parts  of  sulphuric  acid  react  with 

56  parts  of  potassium  hydroxide  and 
40  parts  of  sodium  hydroxide 

to  form  the  primary  sulphates  of  these  metals,  and  with 

112  parts  of  potassium  hydroxide  and 
80  parts  of  sodium,  hydroxide 

to  form  the  secondary  sulphates. 

These  quantities  of  potassium  and  of  sodium  hy- 
droxide are,  however,  in  the  simple  ratio  of  1:2;  so 
that  the  law  of  multiple  proportions  (page  55)  applies 
to  the  more  complicated  processes  of  neutralization  as 
well  as  to  the  comparatively  simple  ones  of  the  union 
of  the  same  two  elements  with  each  other  to  form  more 
than  one  compound. 


64  ELEMENTS   OF  CHEMISTRY. 

Summary. 

1.  Sulphur,  in  burning,  unites  with  oxygen  to  form 
sulphur  dioxide. 

2.  Sulphur    dioxide    can    further   take    up    oxygen, 
under  proper  conditions,  to  form  sulphur  trioxide. 

3.  The    parts    of    oxygen  which  are  united  with  a 
fixed  quantity  of  sulphur  in  these  oxides  are  to  each 
other  as  2 :  3. 

4.  Sulphur  trioxide  unites   with  water  to   produce 
sulphuric  acid.     A  large  amount  of  heat  is  given  off 
during  this  change,  and  the  same  is  true  if  the  acid 
is  diluted  with  water.     Diluted  sulphuric  acid,  conse- 
quentjy,  is  more   difficult  to  decompose  than  concen- 
trated. 

5.  Diluted  sulphuric  acid  when  in  contact  with  cer- 
tain metals  liberates  hydrogen  while  the  corresponding 
sulphates  are  formed.      The  hydrogen  of  the  acid  is 
replaced  by  the  metals. 

6.  Diluted  sulphuric  acid  reacts  with  the  oxides  or 
hydroxides  of   metals    (bases)   to  form  sulphates   and 
water. 

7.  Sulphuric  acid  can  form  two  sulphates   each  of 
sodium  and  of  potassium.      These  sulphates   differ  as 
follows  :   In  one  class  (primary  or  acid  sulphates),  only 
one-half  the  hydrogen  contained  in  the  sulphuric  acid 
from  which  the  salts   are  formed  is  replaced  by  the 
metal.     In  the  other  class  (secondary  or  neutral  sul- 
phates),  all  the    hydrogen  is  replaced   by  the  metal. 
Sulphuric  acid  is*  a  dibasic  acid. 

8.  Hydrochloric  acid  differs  from  sulphuric  acid ;  for 
when  brought  in    contact  with   sodium  or  potassium 
hydroxide  it  forms  but  one  kind  of  chloride,  i.e.,  the 
chloride  produced  by  replacing  all  of  the  hydrogen  of 


THE  OXIDE*k   OF  SULPHUR.  65 

the  hydrochloric  acid  which  is  neutralized.  If  an 
excess  of  hydrochloric  acid  is  present,  this  excess  re- 
mains unaffected  by  the  base.  Hydrochloric  acid  is  a 
monobasic  acid. 

9.  The  sulphates  are  formed  by  the  interaction  of 
definitely  related  amounts  of  base  and  acid. 

10.  The  ratio  between  the  weights  of  various  bases, 
which  are  so  related  in  quantity  that  they  will  exactly 
neutralize  a  given  weight  of  one  acid,  is  also  the  ratio 
by  weight  in  which  these  same  bases  will  exactly  neu- 
tralize a  fixed  amount  of  any  other  acid. 


66  ELEMENTS   OF  CHEMISTRY. 


CHAPTER   X. 

THE   ATMOSPHERE. 

Physical  Properties  of  the  Atmosphere.    The  Barometer.    Boyle's 
and  Charles's  Laws. 

IN  the  previous  portions  of  this  book  mention  has 
been  made  of  the  fact  that  substances  which  burn  in 
oxygen  will  do  the  same  thing,  with  somewhat  dimin- 
ished intensity,  in  the  air.  As  by  far  the  greater  num- 
ber of  combustions  take  place  in  the  latter  medium, 
and  as  it  plays  such  an  important  part  in  the  most  fre- 
quently recurring  chemical  phenomena,  it  is  advisable 
to  become  acquainted  with  the  composition  and  prop- 
erties of  the  atmosphere  at  an  early  period  in  the 
study  of  chemistry.  This  is  the  more  necessary  be- 
cause one  of  its  constituents  (nitrogen)  is  an  element 
with  some  of  whose  compounds  we  must  soon  become 
familiar. 

The  Weight  of  the  Atmosphere.  The  colorless,  gaseous 
envelope  which  surrounds  the  earth  is  termed  its  atmos- 
phere. The  atmosphere,  being  a  material  substance, 
possesses  weight,  and  by  reason  of  this  weight  it  exerts 
a  pressure  on  all  things  beneath  its  surface.  That  this 
is  the  case  can  readily  be  shown  by  the  following  experi- 
ments :  — 

A  piece  of  sheet  rubber  is  tied  over  one  end  of  a 
glass  cylinder,  while  the  other  end,  ground  so  as  to  fit 


THE 


air-tight  over  the  plate  of  an  air-pump,  is"p!aced  over 
the  opening  which  connects  with  the  pump.  The  sheet 
of  rubber  will  be  pressed  inward  as  soon  as  part  of  the 
air  in  the  cylinder  is  exhausted.  Two  hollow  hemi- 
spheres, which  lit  air-tight  along  their  edges,  are  held 
firmly  together  when  the  air  within  them  is  rarefied. 
The  above  phenomena  are  not  observed  until  the  air  is 
exhausted  ;  but  this  is  due  to  the  fact  that  the  atmos- 
phere, being  perfectly  elastic,  presses  equally  in  all 
directions.  It  can,  therefore,  make  its  pressure  mani- 
fest only  when  a  difference  is  established. 

The  Barometer.  If  a  tube  is  entirely  filled  with  liquid,  and 
the  lower  end  is  then  opened  under  the  same  fluid  while  the 
upper  end  remains  closed,  the  liquid  will  not  drop  from  the  tube, 
but  will  remain  in  equilibrium  at  a  certain  height.  This  is  owing 
to  the  pressure  exerted  by  the  surrounding  atmosphere  upon  the 
surface  of  the  fluid  in  the  exterior  vessel.  The  height  of  the 
column  which  can  be  so  maintained  is  inversely  proportional  to 
the  specific  gravity  of  the  liquid  employed.  It.  varies  with  the  at- 
mospheric pressure,  and  is  therefore  used  to  measure  it.  If  a 
tube  is  longer  than  this  column,  then  a  space  containing  no  air 
will  remain  above  the  liquid  in  it.  This  space  is  termed  a  Torri- 
cellian vacuum.  An  instrument  called  the  barometer  is  con- 
structed on  the  above  plan,  the  fluid  in  use  being  mercury  ;  and 
the  distance  from  the  upper  level  of  the  meniscus  of  the  mercury 
in  the  tube  to  the  upper  level  of  that  in  the  container  underneath 
is  termed  the  height  of  the  barometer.  The  mean  height  of  the 
barometer  at  the  level  of  the  sea  is  760  millimetres,  and  this  is 
taken  as  the  standard  for  all  measurements.  The  pressure  exerted 
by  a  column  of  mercury  760  millimetres  high  on  a  square  centi- 
metre is  1.033  kilograms.  The  standard  pressure  of  the  atmos- 
phere upon  the  same  surface  is,  therefore,  equal  to  the  same 
quantity.  If  this  pressure  is  diminished,  the  mercury  will  fall  ; 
if  it  is  increased,  it  will  rise.  If,  therefore,  the  barometer  is  taken 
from  the  sea  level  to  a  point  above  the  same,  a  diminution  in  the 
height  of  the  column  corresponding  to  a  diminution  in  the  weight 


68  ELEMENTS   OF  CHEMISTRY. 

of  the  atmosphere  above  it  will  be  observed.  The  barometric 
height  at  any  place  is  frequently  changing  because  the  atmosphere 
is  not  at  rest,  and  is  subject  to  variations  in  density,  owing  to 
differences  in  temperature.  When  any  portion  of  the  atmosphere 
is  warmed,  its  density  diminishes ;  the  warm  air  will  rise,  its 
pressure  will  diminish,  and,  as  a  consequence,  the  barometer  will 
fall.  The  same  result  is  brought  about  if  the  temperature  re- 
mains constant  while  that  of  contiguous  portions  of  the  atmos- 
phere is  lessened.36 

Relation  of  the  Volume  of  a  Gas  to  Pressure.  If  a  given 
volume  of  air  (V)  is  subjected  to  a  certain  pressure 
(P),  the  volume  will  be  diminished  as  the  pressure  is 
increased.  If  the  second  volume  produced  by  this 
increased  pressure  is  termed  V  and  the  second  pressure 
P',  then  the  relation  — 

V:  V:  :  P' :  P 

will  be  realized.  The  same  is  true  of  all  other  gases 
which,  like  the  atmosphere,  are  at  a  temperature  far 
above  the  point  at  which  they  become  liquid.  This 
fact  can  be  summed  up  in  the  following  law  :  37  — 

Boyle's  Law.  If  the  temperature  remains  constant,  the 
volume  of  a  given  quantity  of  gas  varies  inversely  as 
the  pressure  to  which  it  is  subjected. 

EXAMPLES:  — 

Let  P    =  the  pressure  of  one  atmosphere, 
Let  P '  =  the  pressure  of  two  atmospheres, 
Y    =  10  cubic  centimetres, 

VP      10 
then,  V  =  -p7  =  -o-  =  5  cubic  centimetres.     If  P'  =  3  atmospheres, 

then  V  =  3^  cubic  centimetres,  and  so  on. 

If  P  is  equal  to  the  pressure  of  one  atmosphere,  it  is  equal  to 
the  pressure  exerted  by  760  mm.  of  the  barometer.  If  h  repre- 
sents the  height  in  millimetres  of  the  observed  barometric  pres- 


THE  ATMOSPHERE.  69 

sure,  and  V0  the  volume  of  a  gas  at  760  mm.  pressure,  and  Vt 
that  volume  at  the  observed  pressure,  then,  V0  :  Vt  :  :  h  :  760, 
from  which  it  follows  that  — 

Vt  =—  ^—     '     (Equation  1.) 

Application  of  Boyle's  Law  in  the  Calculation  of  Gas 
Volumes.  To  find  the  volume  which  any  gas  occupies 
at  other  than  the  standard  barometric  pressure,  we  must 
multiply  its  volume  at  the  standard  pressure  by  760,  and 
divide  by  the  observed  height  of  the  barometer. 

From  equation  1  it  follows  that  — 

Vo==~7^     (Equation  2.) 

To  find  the  volume  of  any  gas  at  standard  barometric 
pressure,  we  must  multiply  the  observed  volume  by  the 
observed  barometric  pressure  in  millimetres,  and  divide 
by  760. 

Law  of  Charles  and  Gay  Lussac.  All  gases  when  not 
too  near  the  point  at  which  they  liquefy,  expand  very 
nearly  573  *  of  their  volume  for  each  increase  of  1°  cen- 
tigrade in  temperature.  This  fraction  is  called  the 
co-efficient  of  expansion  of  gases,  and  is  independent 
of  the  pressure  to  which  the  gas  is  subjected. 

EXAMPLES  :  —  A  litre  of  gas  at  0°  will  be  1  +  ^  at  1°,  1  +  373 
at  2°,  ten  litres  would  be  10  +  ^  at  1°,  and  so  on,  so  that  — 

3.  Vt  =  V0  +  V0  «  t 

4.  Vt  =  V0(l  +  «t) 

Vt 


5.    V0  = 


1  -f  at 


where  V0  =  the  volume  of  any  gas  at  0°,  Vt  the  volume  of  the  gas 
at  the  temperature  t,  and  «  =  j|7. 

*  Inexact  numbers  .QQ367. 


70  ELEMENTS   OF  CHEMISTRY. 

To  calculate  the  volume  which  a  gas  would  occupy 
at  0°  (the  standard  temperature),  we  must  divide  the 
observed  volume  by  1  +  «  t. 

When  a  gas  is  at  ordinary  temperature  and  pressure,  and  we 
wish  to  ascertain  its  volume  at  standard  barometric  pressure  (7  GO 
millimetres)  and  temperature  0°,  corrections  must  be  made  both 
for  temperature  and  pressure.  This  can  be  done  in  one  operation 
by  combining  equations  2  and  5,  which  gives  — 


6.   Vo= 


760(1  +  at) 


If  a  gas  is  introduced  into  the  Torricellian  vacuum  so  that  a 
part  of  the  mercury  is  expelled  from  the  tube,  this  gas  is  obviously 
under  atmospheric  pressure,  minus  the  height  of  the  mercury  still 
in  the  tube.  If  this  latter  quantity  is  w,  then  equation  6  becomes  — 


y 

" 


760(1  +  at) 


Standard  Conditions  for  the  Measurement  of  Gas  Volumes. 
A  gas  at  temperature  0°  and  pressure  760  millimetres 
is  said  to  be  under  standard  conditions  ;  and  all  com- 
parisons between  the  volumes  of  different  gases  pre- 
suppose that  these  volumes  are  under  those  conditions, 
unless  the  contrary  is  expressly  stated. 

Vapor  Pressure  and  Correction  for  the  same.  Gases  which  are 
undergoing  observation  may  contain  water.  If  this  is  the  case,  a 
further  correction  must  be  made  for  the  pressure  of  the  vapor  of 
water,  since  it  is  obvious  that  this  vapor  exerts  a  pressure  which 
increases  with  the  temperature  exactly  as  does  that  of  the  gas 
which  is  to  be  measured.  This  amount,  in  millimetres,  must 
therefore  be  deducted  from  the  observed  barometric  height,  so  that 
equation  7  becomes  — 

yt(h-w-*) 
760(1  +  at) 

where  <*>  represents  the  vapor  pressure  in  millimetres  at  the  tem- 
perature of  observation.     What  is  true  of  water  vapor  is  true  of 


THE  ATMOSPHERE.  71 

the  vapors  of  other  liquids  as  well,  with  the  distinction  that  at  the 
same  temperature  the  vapors  of  different  liquids  exert  different 
pressures.*  As  a  matter  of  fact,  water  vapor  and,  at  high  tem- 
peratures, the  vapor  of  mercury,  are  the  only  ones  to  be  consid- 
ered in  elementary  work.88 

*  A  table  giving  the  tension  of  water  vapor  at  different  temperatures 
can  always  be  found  in  the  larger  manuals  of  chemistry,  or  in  small  vol- 
umes of  "tables"  for  chemists.  One  of  the  latter  should  always  be 
easily  accessible. 


72  ELEMENTS   OF  CHEMISTRY. 


CHAPTER   XI. 

THE  ATMOSPHERE   (Continued). 
Combustion  in  Oxygen  and  in  Air. 

Isolation  of  Nitrogen  from  the  Atmosphere.  Heat  to  red- 
ness a  long  tube  containing  a  quantity  of  fine  copper 
shavings.  Pass  air  through  this  tube,  and  collect  the 
gas  that  emerges  in  a  tube  closed  at  one  end,  filled 
with  water  and  inverted  in  a  water  trough.  This  gas 
will  be  found  to  differ  in  properties  from  the  air  which 
originally  contained  it.  It  is  colorless  and  odorless. 
A  burning  pine  splinter  placed  in  it  is  instantly  extin- 
guished. At  the  same  time,  unlike  hydrogen,  it  does 
not  itself  burn.  This  gas  is  an  element  and  is  termed 
nitrogen. 

Properties  of  Nitrogen.  Nitrogen  has  a  specific  gravity  (air  ||  1) 
of  .97209.  At  a  pressure  of  35  atmospheres  and  at  temperature 
of  — 146°.3  it  becomes  liquid.  This  liquid  boils  at— 193° and 
solidifies  at  —  203°.  Chemically,  nitrogen  in  a  free  state  is  a  re- 
markably indifferent  substance,  uniting  with  other  elements  only 
under  the  greatest  provocation.  Owing  to  this  indifference,  it  will 
neither  burn  nor  support  combustion,  and  animals  are  suffocated 
when  placed  in  it. 

The  Atmosphere  contains  Nitrogen  and  Oxygen.  The  hot 
copper  over  which  the  air  was  passed  is  completely 
changed,  and  at  the  same  time  it  has  gained  in  weight. 
The  same  alteration  in  the  copper  can  be  brought  about 


THE  ATMOSPHERE.  73 

by  heating  it  in  pure  oxygen.  Hence,  we  conclude  that 
in  the  above  experiment  it  has  been  oxidized  by  the 
air  to  form  copper  oxide.  The  atmosphere,  therefore, 
contains  nitrogen  and  oxygen.39 

Combustion  in  Oxygen.  Oxygen  is  a  supporter  of  com- 
bustion. This  means  that  many  substances,  if  they  are 
heated  in  the  gas  to  points  above  their  kindling  temper- 
atures, will  unite  with  it  energetically,  evolving  heat 
and  light  (see  page  36).40 

EXAMPLES  :  —  A  small  piece  of  phosphorus,  if  ignited  in  the  air 
and  placed  in  a  jar  of  oxygen,  will  burn  with  dazzling  brilliancy, 
the  product  of  the  combustion  being  an  oxide  of  phosphorus 
(phosphorus  pentoxide). 

Sulphur,  ignited  in  the  air,  will  burn  energetically  in  oxygen, 
producing  an  oxide  of  sulphur  (sulphur  dioxide  ;  see  page  53).  A 
piece  of  charcoal  heated  to  redness  will  burn  brightly  in  oxygen, 
the  resulting  compound  being  an  oxide  of  carbon  (carbon  dioxide). 

In  the  same  way  many  other  elements,  sodium,  potassium, 
magnesium,  will  burn  in  oxygen  with  the  greatest  energy,  while 
in  each  case  the  corresponding  oxide  is  produced  ;  and  even  sub- 
stances which  under  ordinary  circumstances  are  considered  as 
being  non-combustible  (for  example,  a  steel  watch-spring)  can  be 
ignited  in  oxygen. 

Changes  of  Energy  during  Combustion.  The  cause  un- 
derlying all  these  phenomena  is  the  same,  and  is  iden- 
tical with  the  one  discussed  when  we  studied  the 
formation  of  water  during  the  combustion  of  hydrogen 
in  oxygen.  The  substances  which  burn  all  possess 
chemical  energy  when  in  the  presence  of  oxygen.  This 
chemical  energy  is  converted  into  kinetic  energy  (light 
and  heat)  during  the  combustion,  so  that  the  resulting 
bodies  possess  less  energy  than  do  the  substances  from 
which  they  are  produced.  Obviously,  therefore,  as 


74  ELEMENTS   OF  CHEMISTRY. 

mucn  energy  would  have  to  be  added  to  decompose 
these  substances  as  is  given  off  in  their  formation, 
provided  equal  quantities  of  matter  are  considered  in 
each  case  (see  page  34). 

Slow  Oxidation.  Oxidation  may  take  place  so  slowly 
that  the  heat  given  off  during  any  given  time  is  too 
small  to  be  observed  by  the  senses,  and  can  be  measured 
only  by  apparatus  specially  constructed  for  the  purpose. 
The  total  amount  of  kinetic  energy  manifested  during 
such  a  change  is,  however,  the  same  as  it  would  be 
were  the  same  amount  of  the  same  substance  burned 
rapidly,  provided  that  the  oxides  produced  are  identical. 
The  amount  of  energy  employed  to  decompose  a  given 
quantity  of  these  oxides  is  unvarying,  no  matter  whether 
they  have  been  produced  rapidly  or  slowly.  A  parallel 
condition  is  found  in  that  of  a  weight  which  has  been 
lowered  from  a  height.  It  obviously  requires  a  certain 
expenditure  of  energy  to  bring  this  weight  back  to  its 
original  position,  and  this  expenditure  is  entirely  inde- 
pendent of  the  circumstances  attending  the  fall.  We 
have  already  seen  that  the  heat  given  off  during  the 
formation  of  a  chemical  compound  is  equivalent  to  the 
amount  of  energy  necessary  for  its  decomposition  (see 
page  34). 

Incandescence  during  Combustion.  Production  of  a  Flame. 
The  phenomena  of  combustion  are,  therefore,  caused 
by  the  union  of  certain  substances  with  oxygen,  the 
change  taking  place  in  so  short  an  interval  of  time  that 
the  heat  caused  by  the  reaction  is  not  conducted  away 
with  sufficient  rapidity,  and  raises  the  temperature  to  a 
point  at  which  the  burning  body  becomes  incandescent. 


THE  ATMOSPHERE.  75 

When  the  ignited  substance  is  a  gas,  or  when  in  burn- 
ing it  either  gives  off  a  gas  or  is  converted  into  a  gas, 
a  flame  is  produced,  as  in  the  case  of  the  burning  of 
phosphorus  or  sulphur.  On  the  other  hand,  when  no 
vapor  is  present,  the  burning  substance  simply  glows, 
as  is  seen  during  the  combustion  of  carbon.  A  flame 
is,  therefore,  developed  by  an  incandescent  gas. 

The  Phenomena  of  Gaseous  Combustion  are  Reversible. 
Where  a  gas  is  capable  of  uniting  with  oxygen  with 
sufficient  energy  to  produce  a  flame,  it  is  a  matter  of 
indifference  which  of  the  two  gases  forms  the  entering, 
and  which  the  surrounding  medium,  since  the  phenom- 
ena of  combustion  are  caused  solely  by  the  chemical 
union  of  the  two.  The  terms  "combustible"  and  "a 
supporter  of  combustion,"  as  applied  to  gases,  are  used 
simply  because  it  is  more  usual  to  see  gases  burning  in 
oxygen  or  air  than  it  is  to  see  oxygen  or  air  burning  in 
other  gases.41 

EXAMPLES  :  —  Hydrogen  burns  quite  readily  in  oxygen  with  a 
very  hot  flame,  and,  vice  versa,  oxygen  will  burn  in  hydrogen 
with  an  equally  hot  flame.  In  both  instances  water  is  produced. 
Sulphur  will  burn  in  oxygen,  and,  on  the  other  hand,  oxygen  will 
burn  in  the  vapor  of  sulphur,  the  same  oxide  of  sulphur  being 
formed  in  each  case. 

Union  with  Oxygen  is  not  Necessary  to  cause  Incandescence. 
Any  two  elements  which  are  capable  of  directly  uniting, 
give  off  heat  during  such  union  ;  and  this  heat  may  be 
sufficient  to  cause  both  substances  to  become  incan- 
descent. 

EXAMPLES  :  —  Hydrogen,  when  heated  to  its  kindling  tempera- 
ture, will  readily  burn  in  an  atmosphere  of  chlorine,  the  product 


76  ELEMENTS   OF  CHEMISTRY. 

being  hydrogen  chloride  ;  and,  of  course,  chlorine  will  also  burn 
in  hydrogen. 

Phosphorus  is  capable  of  burning  in  chlorine  to  form  a  chloride 
of  phosphorus,  just  as  it  will  burn  in  oxygen  to  form  an  oxide. 

Iron  filings,  when  mixed  with  finely  divided  sulphur,  will 
unite  with  the  latter  with  the  greatest  energy,  if  sufficient  heat  is 
applied  to  melt  the  sulphur,  and  thereby  cause  an  intimate  contact 
between  the  two  elements.  The  mixture  becomes  brightly  incan- 
descent, and  sulphide  of  iron  is  formed  as  a  product  of  the  re- 
action.f5  *. 

General  Nature  of  the  Phenomena  of  Combustion.  The 
phenomena  of  combustion  in  oxygen  are  therefore 
merely  special  cases  of  chemical  reactions  which  are 
very  general  in  their  character.  The  fact  that  enough 
heat  is  given  off  during  these  changes  to  cause  the 
reacting  elements  to  glow  is  incidental,  and  not  essen- 
tial to  the  character  of  the  phenomena  as  a  whole.  The 
essential  feature  is  that  elements  which  are  capable  of 
direct  union  possess  chemical  energy,  and  this  chemical 
energy  is  converted  into  kinetic  energy  when  such 
union  takes  place.  We  have  two  conditions  in  which 
the  elements  can  be  encountered :  — 

1.  Those  in  which  they  are  chemically  separate  ; 

2.  Those  in  which   they  are  chemically  combined; 
and   if    the   union    of    the    elements    can   be    brought 
about  without  the  addition   of  external    energy,   then 
those   substances    under  the  second  head  possess  less 
chemical  energy  than  do  those  under  the  first. 

Enduring  Nature  of  Chemical  Energy.  Chemical  energy 
is  a  most  enduring  form  of  energy.  A  piece  of  coal 
or  of  sulphur  may  remain  buried  in  the  earth  for  years 
without  the  least  loss  of  the  power  which  these  sub- 
stances are  capable  of  yielding  when  burned.  Chem- 


THE  ATMOSPHERE.  77 

ical  energy  is  also  the  most  concentrated  form  of  energy. 
The  amount  of  heat  given  off  by  the  combustion  of  one 
gram  of  hydrogen  would  be  capable  of  raising  14,000 
kilograms  through  the  distance  of  one  metre  if  this 
heat  could  be  completely  converted  into  mechanical 
work.  At  the  present  time  no  other  form  of  energy 
combines  so  great  convenience  and  permanence  in 
transportation  as  does  chemical.  Steamboats  crossing 
the  ocean  take  along  their  stock  of  chemical  energy  in 
the  form  of  coal,  which,  by  the  heat  given  off  in  its  com- 
bustion, furnishes  the  power  to  propel  the  vessel.  In 
former  geologic  periods  the  flourishing  vegetation  stored 
up  this  force  by  making  use  of  the  radiating  energy  of 
the  sun  ;  this  vegetation  was  destroyed,  buried  by  the 
debris  of  succeeding  catastrophes,  and  is  now,  in  the 
form  of  coal,  finding  its  uses  in  the  daily  avocations  of 
men.* 

Chemical  Energy  is  also  possessed  by  Chemical  Compounds. 
The  separate  elements  which  are  capable  of  chemical 
union  are  not  the  only  forms  of  matter  which  possess 
chemical  energy.  Many  chemical  compounds  also  unite, 
with  the  evolution  of  heat  and  even  of  light,  to  produce 
new  compounds  possessing  less  chemical  energy  than 
did  those  from  which  they  were  formed.  We  have 
studied  examples  of  such  changes  in  the  neutralization 
of  acids  by  bases,  and  in  the  union  of  salts  with  their 
water  of  crystallization.  Tn  short,  the  tendency  of 
substances  which  possess  chemical  energy  is  so  to  inter- 
act with  each  other  as  to  transform  the  whole  or  a  part 
of  that  chemical  energy  into  kinetic  energy,  or,  in  other 

*  This  paragraph  is  in  part  taken  from  Ostwald,  Lehrbuch  der  Allge- 
meinen  Chemie,  2],  53.  » 


78  ELEMENTS   OF  CHEMISTRY. 

words,  to  pass  from  a  state  of  higher  energy  to  one  of  a 
lower.  Those  changes  attendant  on  combustion  of  oxy- 
gen are,  therefore,  only  specific  cases  of  what  in  reality 
is  most  general  in  chemistry.  They  have  assumed  such 
great  relative  importance  only  because  of  the  general 
distribution  of  the  element  oxygen,  and  because  of  its 
essential  bearing  upon  life.  From  a  scientific  point  of 
view,  any  one  of  the  parallel  chemical  reactions  in 
which  the  union  of  elements  is  attended  with  the  evo- 
lution of  light  and  of  heat  is  as  important  in  illustrat- 
ing a  general  law  as  is  the  union  of  elements  with 
oxygen.43 

Combustion  in  Air.  Substances  which  burn  in  oxygen 
will  also  burn  in  the  air,  but  with  diminished  intensity, 
owing  to  the  fact  that  the  oxygen  is  diluted  by  the  in- 
different gas,  nitrogen.  If  the  combustion  takes  place 
in  a  closed  space,  it  will  continue  until  all,  or  nearly  all, 
the  oxygen  is  used  up,  and  then,  provided  the  products 
of  combustion  are  solid,  nothing  but  nitrogen  will 
remain. 

EXAMPLES  :  —  A  piece  of  phosphorus  ignited  and  placed  in  a 
closed  jar  of  air  will  continue  to  burn  until  the  oxygen  is  ex- 
hausted. The  oxide  of  phosphorus  produced  in  this  way  is 
identical  with  the  one  formed  in  oxygen.  The  gas  which  remains 
has  all  of  the  properties  of  nitrogen  ;  it  will  neither  burn  nor  sup- 
port combustion. 

A  burning  candle  placed  in  a  closed  air-space  will  gradually 
be  extinguished  after  using  up  the  available  oxygen.  The  gases 
which  remain  consist  of  nitrogen,  carbon  dioxide,  and  some 
oxygen.* 

*  All  the  oxygen  is  not  used  by  the  burning  candle,,or  by  an  animal 
placed  in  a  closed  air-space.  The  extinction  of  the  flame  and  asphyx- 
iation take  place  while  a  considerable  quantity  of  oxygen  is  still 
uncombined. 


THE  ATMOSPHERE.  79 

This  mixture  will  neither  burn  nor  support  the  combustion  of  a 
candle.44 

An  animal  placed  in  a  closed  air-space  will  become  unconscious 
and  finally  die.  The  oxygen  inhaled  by  the  lungs  is  in  part  ab- 
sorbed by  the  blood,  and  is  used  in  the  body  for  purposes  of  oxi- 
dization. As  the  tissues  of  the  body  consist  mostly  of  compounds 
of  the  element  carbon  with  hydrogen,  nitrogen,  sulphur,  etc.,  the 
products  of  this  oxidization  are  in  large  part  carbon  dioxide  and 
water  vapor.  The  air  exhaled  from  the  lungs  contains  less  oxy- 
gen and  more  carbon  dioxide  than  does  that  which  is  inhaled. 
All  the  oxygen  taken  in,  however,  is  not  consumed  in  the  produc- 
tion of  these  two  gases ;  for  there  are  other  constituents  of  the 
body  (sulphur,  phosphorus)  which  are  also  oxidized  and  separated 
by  different  channels,  while  a  portion  of  the  oxygen  is  returned 
to  the  air  unchanged.  As  the  oxygen  of  the  air  becomes  used  up 
by  a  breathing  animal,  and  is  in  part  replaced  by  carbon  dioxide, 
the  closed  air-space  becomes  unfit  for  the  support  of  animal  life 
long  before  all  of  the  oxygen  is  consumed.  This  takes  place  the 
more  rapidly  because,  in  addition  to  the  substances  mentioned, 
there  are  other  gases  of  a  poisonous  nature  exhaled  from  the 
lungs. 

The  Process  of  Breathing  is  Analogous  to  Combustion. 
The  process  of  breathing  can,  therefore,  be  compared 
to 'combustion.  The  animal  and  the  surrounding  oxy- 
gen possess  chemical  energy  which  is  converted  into 
kinetic  energy  •  by  respiration  and  its  consequences. 
This  kinetic  energy  is  manifested  as  heat,  so  that  the 
body  preserves  a  temperature  above  that  of  the  sur- 
rounding atmosphere,  while  the  substances  produced 
possess  much  less  chemical  energy  than  did  those  which 
were  originally  present. 

The  Total  Heat  given  off  in  Combustion  in  Air  is  the 
same  as  that  given  off  in  Combustion  in  Oxygen.  A  num- 
ber of  other  examples  of  combustion  in  air  could  be 
mentioned;  but,  as  they  do  not  differ  in  principle  from 


80  ELEMENTS   OF  CHEMISTRY. 

combustion  in  oxygen,  it  is  not  necessary  to  enumerate 
them.  The  total  amount  of  heat  given  off  during  the 
combustion  of  a  given  weight  of  a  substance  is  the  same, 
whether  it  is  burned  in  air  or  in  oxygen.  This  fact  is 
obvious  when  we  consider  that  it  will  take  exactly  as 
much  energy  to  decompose  the  body  which  is  formed 
as  has  been  given  off  in  its  production.  The  amount 
necessary  for  this  decomposition  is  manifestly  independ- 
ent of  the  circumstances  surrounding  the  formation. 


THE  ATMOSPHERE.  81 


CHAPTER   XII. 

THE  ATMOSPHERE  (Continued). 
Composition  of  the  Atmosphere. 

WE  have  learned  that  the  atmosphere  contains 
oxygen  and  nitrogen,  but  we  have  not  ascertained  the 
relative  proportion  of  the  two  gases,  nor  have  we  de- 
cided whether  they  are  chemically  combined  or  present 
merely  as  a  mechanical  mixture. 

Estimation  of  the  Relative  Amounts  of  Oxygen  and  Ni- 
trogen in  the  Atmosphere.  A  rough  means  of  estimating 
the  amount  of  oxygen  and  nitrogen  in  the  atmosphere 
is  found  in  the  following  experiment :  — 

A  glass  tube  sealed  at  one  end  is  divided  into  five  equal  parts 
by  means  of  five  rubber  rings  slipped  over  the  outside.  This  is 
inverted  over  a  cylinder  of  water  so  that  the  level  of  the  liquid 
within  and  without  is  at  the  first  ring,  and  the  tube  is  then 
firmly  clamped  in  this  position.  A  piece  of  phosphorus  is  fixed 
on  the  end  of  a  long,  sharp-pointed  wire,  and  then  the  wire  is 
bent  so  that  the  phosphorus  can  be  thrust  up  into  the  tube. 
Slow  oxidization  of  the  phosphorus  will  set  in,  and  the  oxide  of 
phosphorus  produced  will  be  dissolved  by  the  water,  which  will 
rise  in  the  tube  so  as  to  take  the  place  of  the  oxygen  absorbed. 
The  reaction  is  complete  after  some  days  ;  and  then  it  will  be  dis- 
covered, after  the  tube  has  been  lowered  so  that  the  level  of  the 
liquid  without  and  within  is  again  the  same,  that  four-fifths  of 
the  air  have  remained  unabsorbed.  Approximately,  therefore,  by 


82  ELEMENTS   OF  CHEMISTRY. 

bulk  one-fifth  of  the  atmosphere  consists  of  oxygen,  and  four-fifths 
of  nitrogen.45 

More  accurate  results  can  be  obtained  by  the  use  of  the  eudi- 
ometer tube  (described  on  page  24,  and  in  Experiment  10  of  the 
Appendix).  This  is  filled  with  so  much  mercury,  that,  when  it  is 
inverted  over  the  mercury  trough,  about  fifteen  cubic  centimetres 
of  air  will  remain  enclosed.  This  volume  is  recalculated  to 
standard  conditions  by  noting  the  temperature,  barometric  pres- 
sure, and  height  of  the  column  of  mercury  above  the  trough 
(see  page  68  and  following).  About  seven  cubic  centimetres  of 
pure  hydrogen  are  now  added ;  and  the  volume  of  this  gas  is  also, 
after  making  the  necessary  observations,  recalculated  to  standard 
conditions.  The  mixture  is  now  exploded  by  means  of  an  electric 
spark.  The  contraction  in  volume  which  results  is  due  to  the  for- 
mation of  water  from  the  union  of  hydrogen  and  oxygen;  and 
as  two  volumes  of  hydrogen  combine  with  one  of  oxygen  to 
produce  water,  it  follows  that  one-third  of  the  total  diminution 
in  volume  must  represent  the  amount  of  oxygen  which  was  ori- 
ginally present.46 

Relative  Volume  of  Oxygen  and  Nitrogen  in  the  Atmosphere. 
Careful  investigations  by  this  means  have  shown  that 
the  volume  of  oxygen  in  ordinary  out-door  air  varies 
from  20.3  to  21.5  volumes  in  100.*  This  variation 
is  sufficient  to  show  us  that  in  all  probability  the  at- 
mosphere is  not  a  chemical  compound;  for,  as  we  have 
seen,  true  chemical  compounds  are  characterized  by  an 
unchanging  composition  (see  page  55).  This  proba- 
bility is  transformed  to  a  certainty  by  the  following 
experiment :  — 

Proofs  that  the  Atmosphere  is  not  a  Chemical  Compound. 
A  given  volume  of  water  will  dissolve  quite  a  little 
more  oxygen  than  nitrogen,  so  that  if  we  collect  the 

*  I.e.,  in  100  cubic  centimetres  of  air  there  are  20.3  to  21.5  cubic 
centimetres  of  oxygen. 


THE  ATMOSPHERE.  83 

gas  which  passes  off  from  water  which  has  been  ex- 
posed to  the  air  under  pressure,  it  will  contain  a  greater 
proportion  of  oxygen  than  it  did  before.  Using  the 
air  which  has  thus  been  altered  in  composition,  this 
operation  can  be  repeated  with  a  similar  result  until 
nearly  pure  oxygen  is  finally  obtained. 

As  a  final  proof  it  may  be  mentioned  that  oxygen 
and  nitrogen,  mixed  in  the  proper  proportions,  form  air 
without  alteration  either  in  the  total  volume  of  the 
two  gases  or  of  the  temperature,  provided  they  were 
under  like  conditions  before  being  brought  in  contact. 
The  atmosphere  is,  therefore,  a  mechanical  mixture  of 
oxygen  and  nitrogen,  containing  in  round  numbers  one 
part  by  volume  of  the  former  to  four  parts  of  the 
latter. 

Other  Substances  Present  in  the  Atmosphere.  In  addi- 
tion to  the  two  fundamental  gases,  other  substances 
are  present  in  the  air  in  small  quantities.  These  may 
be  of  two  kinds,  —  gaseous  and  solid.  The  chief  gas- 
eous impurities  are  water  vapor,  carbon  dioxide  (see 
page  154),  and  compounds  of  ammonium  (see  page 
99).  The  solid  substances  are  present  as  dust. 

Water  Vapor  in  the  Atmosphere.  The  quantity  of  water  vapor 
present  depends  upon  the  temperature,  season  of  the  year,  and 
locality ;  but  it  is  seldom  of  sufficient  amount  to  cause  the  atmos- 
phere to  be  completely  saturated.  The  evaporation  of  oceans, 
lakes,  and  rivers,  furnishes  a  never-ending  supply  of  water,  which 
is  increased  by  hot  weather,  and  is  generally  greater  by  day  than 
by  night.  If  the  atmosphere  is  nearly  saturated  with  moisture, 
any  diminution  in  the  temperature  will  cause  a  fall  of  rain  or  the 
formation  of  dew.  Very  little  evaporation  can  take  place  while 
such  a  condition  prevails.  Drops  of  water  collect  upon  a  cold 
surface  because  the  air  in  the  immediate  neighborhood  is  cooled 


84  ELEMENTS   OF  CHEMISTRY. 

below  the  point  at  which  it  is  saturated  with  vapor.  The  tem- 
perature at  which  these  drops  collect  is  called  the  dew-point ;  and 
as  the  maximum  amount  of  water  vapor  which  can  be  contained  in 
a  given  volume  of  the  atmosphere  at  any  definite  temperature  is 
known,  the  discovery  of  the  dew-point  affords  a  ready  means  of 
ascertaining  the  amount  of  moisture  really  present  in  the  air. 
The  ratio  between  the  tension  of  water  vapor  (see  page  70), 
which  would  be  found  were  the  air  fully  saturated  at  the  prevail- 
ing temperature,  and  that  tension  which  really  exists,  is  called 
the  relative  humidity.47 

Water  in  the  atmosphere  is  absolutely  essential  to  plant  life. 
The  liquid  falls  upon  the  soil  as  rain,  and  is  absorbed  by  the 
radicles  of  plants.  Afterwards  it  circulates  through  the  entire 
system  of  the  plant,  taking  part  in  various  physiological  changes, 
and  finally  evaporating  from  the  leaves.  The  amount  of  moisture 
which  passes  from  large  areas  covered  by  vegetation  is  enormous, 
so  that  wooded  districts  cause  an  equitable  distribution  of  rain. 

Carbon  Dioxide  in  the  Atmosphere.  Carbon  dioxide  is  invari- 
ably found  in  the  air,  and  is  as  important  to  living  organisms  as 
oxygen  itself.  It  is  constantly  added  to  the  atmosphere  by  burn- 
ing fuel,  from  volcanic  craters  and  fissures,  from  the  breathing 
of  animals,  and  from  decomposing  organic  matter.  If  no  means 
were  provided  for  the  removal  of  carbon  dioxide  from  the  atmos- 
phere, the  increase  would  soon  destroy  all  living  organisms  de- 
pendent upon  respiration.  Fortunately  plants  growing  in  the 
sunlight  absorb  carbon  dioxide  from  the  air,  using  for  this  ab- 
sorption a  green  coloring-matter  which  is  contained  in  the  leaves, 
and  which  can  eliminate  oxygen  from,  and  add  hydrogen  to,  car- 
bon dioxide.  By  this  means  a  substance  is  produced  which  can 
form  all  the  innumerable  compounds  of  carbon,  hydrogen,  and 
oxygen  occurring  in  the  vegetable  kingdom.48 

The  Quantity  of  Carbon  Dioxide  in  the  Atmosphere.  The 
quantity  of  carbon  dioxide  in  a  given  volume  of  air 
varies  slightly ;  but,  normally,  it  is  about  three  parts  in 
ten  thousand.  It  seems  that  the  proportion  of  carbon 
dioxide  is  greater  at  night  than  in  the  daytime,  and  in 


THE  ATMOSPHERE.  85 

summer  than  in  winter.  The  amount  of  carbon  dioxide 
in  crowded  rooms  is  increased  by  the  breathing  of  peo- 
ple within  the  closed  air-space,  yet  this  does  not  often 
take  place  to  such  an  extent  that  the  oppressive  feeling 
caused  by  such  an  atmosphere  can  be  ascribed  entirely 
to  this  increase.  The  unpleasant  effect  is  due  in  part 
to  exhalations  of  organic  matter  which  passes  off  from 
the  lungs. 

The  presence  of  oarbon  dioxide  in  the  atmosphere  can  be 
proved  at  any  time  by  exposing  some  clear  lime-water  to  the 
action  of  the  air.  If  carbon  dioxide  is  present,  a  white  crust  of 
the  carbonate  of  calcium  will  be  found  upon  the  surface  in  a 
short  time. 

Ammonia  in  the  Atmosphere.  Another  impurity  present  in 
the  atmosphere  is  ammonia,  which  is  found  combined  with  acids, 
as  ammonium  carbonate,  nitrate,  or  nitrite.  These  substances  are 
washed  into  the  soil  by  rains,  and  are  then  taken  up  by  plants  to 
form  essential  portions  of  their  tissues  which  contain  nitrogen. 
The  amount  of  ammonium  compounds  in  the  atmosphere  is  very 
small,  not  more  than  forty  parts  by  weight  in  one  million  parts  of 
air. 

The  solid  particles  of  dust  floating  in  the  air  may  be 
such  substances  as  common  salt  (sodium  chloride),  or 
they  may  consist  of  micro-organisms,  which  not  infre- 
quently are  capable  of  inaugurating  disease. 

Summary  of  the  Chapters  on  the  Atmosphere. 

1.  The  atmosphere  is  composed  of  oxygen  and  nitro- 
gen, with  small  quantities  of  other  substances.     (Carbon 
dioxide,  water  vapor,  ammonium  salts,  solid  particles.) 

2.  Nitrogen   is    chemically  an  indifferent  gas,   and 
does  not  support  combustion. 

3.  Oxygen  is  a  supporter  of  combustion ;   i.e.,  many 
substances  will  burn  in  the  gas,  producing  oxides. 


86  ELEMENTS   OF  CHEMISTRY. 

4.  Substances  which  burn  possess  chemical  energy 
when  in  the  presence  of  oxygen.     This  chemical  energy 
is  converted  into  kinetic  energy  during  the  combustion. 

5.  The  substances  produced  by  the  union  possess  less 
chemical  energy  than  do  those  from  which   they  are 
formed. 

6.  Oxidation  may  be  slow  or  rapid.      The  amount 
of  chemical  energy  converted  into  kinetic  energy  is, 
however,  the  same  in  either  case,  provided  the  amounts 
of  the  substances  used  are  the  same  and  the  products 
of  combustion  are  identical. 

7.  In  rapid  combustion  the  temperature  is  raised  to 
a  point  at  which   the    reacting   body  becomes    incan- 
descent.    If  the  burning  substance  is  a  gas,  or  gives 
off  a  gas,  then  a  flame  is  produced.     It  is  a  matter  of 
indifference  which  gas  is  entering,  and  which  forms  the 
surrounding  medium,  the  combustion  taking  place  just 
the  same  in  either  case. 

8.  The  phenomena  of  combustion  in  oxygen  are  only 
special  cases  of  chemical  reactions  which  are  general  in 
their  character;    similar  changes,  therefore,  take  place 
when  bodies  unite  with  substances  other  than  oxygen. 

9.  We  have  two  conditions  in  which  the  elements 
are  encountered,  —  those  in  which  they  are  chemically 
separate,  and  those  in  which  they  are  chemically  com- 
bined.    The  separate  elements  are  not  the  only  forms 
of  matter  which  possess   chemical  energy.      Chemical 
compounds  can  also  unite,  with  the  evolution  of  light 
and  heat. 

10.  Substances  which  burn  in  oxygen  will  also  burn 
in  air  with  diminished  brilliancy.     The  process  of  breath- 
ing can  be  compared  to  combustion. 

11.  The  total  amount  of  heat  given  off  during  the 


THE  ATMOSPHERE.  87 

combustion  of  a  given  weight  of  a  body  Is  the  same 
whether  it  is  burned  in  air  or  in  oxygen. 

12.  The  oxygen  in  the  atmosphere  varies  from  20.3 
to  21.5  volumes  in  100.     The  air  is  a  mixture  of  oxy- 
gen and  nitrogen,  and  not  a  chemical  compound. 

13.  The  air  contains  water  vapor  in  varying  amounts, 
—  carbon  dioxide  in  about  three  parts  in  ten  thousand, 

and  very  small  quantities  of  ammonium  compounds  and 
of  solid  substances. 


88  ELEMENTS   OF  CHEMISTRY. 


CHAPTER   XIII. 

THE  COMPOUND  OF  HYDROGEN  AND  NITROGEN. 
(AMMONIA.) 

THE  not-metallic  elements  which  have  been  discussed 
(oxygen  and  chlorine)  unite  with  hydrogen  to  form 
water  and  hydrogen  chloride  respectively.  Naturally, 
then,  in  studying  nitrogen  we  ask  if  it  also  will  combine 
with  hydrogen,  and  if  it  does,  what  the  nature  of  the 
resulting  compound  is. 

Direct  Union  of  Nitrogen  and  Hydrogen  Difficult.  The 
chemically  indifferent  nature  of  nitrogen  becomes  appar- 
ent when  we  make  the  attempt  to  bring  about  its  union 
with  hydrogen.  If  an  electric  spark  is  passed  through 
a  mixture  of  hydrogen  and  nitrogen  no  explosion  takes 
place,  and  even  if  the  operation  is  continued  for  some 
time  the  elements  will  be  found  to  have  united  only  in 
the  smallest  quantity.  The  direct  union  of  the  elements, 
therefore,  affords  us  no  practical  method  for  the  prepara- 
tion of  the  hydrogen  compound  of  nitrogen,  but  we  can 
easily  obtain  it  by  other  means. 

The  Preparation  of  Pure  Ammonia.  Concentrated  commercial 
ammonia  water  is  placed  in  a  flask,  so  arranged  that  any  gases 
evolved  can  be  passed  through  a  tube  containing  pieces  of  quick- 
lime, to  a  vessel  containing  mercury,  in  which  is  placed  a  glass 
tube,  closed  at  one  end,  filled  with  the  same  liquid,  and  in- 


COMPOUND    OF  HYDROGEN   AND   NITROGEN.     89 

verted.*  The  quick-lime  is  introduced  for  the  purpose  of  drying 
the  gas  which  passes  off  as  soon  as  the  flask  is  gently  warmed. 
This  gas  can  be  collected  above  the  mercury  in  the  inverted 
tube.f  49 

Properties  of  Ammonia.  The  gas  isolated  in  this  way  is  termed 
ammonia.  It  has  a  specific  gravity,  air  =  1,  of  .589  ;  and,  being 
relatively  lighter  than  air,  it  can  be  collected  by  passing  it 
through  a  long  tube  extending  up  to  the  bottom  of  an  empty  jar 
held  mouth  downward.  This  method  is  convenient  if  absolutely 
pure  ammonia  is  not  required.  Ammonia  becomes  liquid  at  a 
temperature  of  —  40°  under  a  pressure  of  one  atmosphere.  One 
cubic  centimetre  of  water  is  capable  of  dissolving  813  cubic  cen- 
timetres of  ammonia,  and  it  is  owing  to  its  extreme  solubility  in 
water  that  we  are  compelled  to  collect  the  gas  over  mercury. 

Commercial  ammonia  is  simply  a  solution  of  ammonia  gas  in 
water;  we  have  learned  (page  16)  that  gases  are  less  soluble  the 
higher  the  temperature  of  the  liquid  in  which  they  are  dissolved. 
Ammonia  gas  is,  therefore,  evolved  when  ammonia  water  is 
heated,  and  the  above  experiment  for  the  isolation  of  ammonia 
is  based  upon  this  fact.60 

Decomposition  of  Ammonia.  The  first  question  which 
we  must  decide  in  regard  to  ammonia  is  whether  the 
gas  is  an  element  or  a  compound.  A  method  of  de- 
composition suggests  itself  similar  to  those  employed  in 
the  study  of  water  and  of  hydrogen  chloride  ;  i.e.,  to  see 
whether  ammonia  is  decomposed  by  sodium  or  potas- 
sium. These  experiments  are  not  so  easily  carried  out 
in  this  case  as  they  were  with  the  substances  previously 
studied,  for  if  sodium  or  potassium  is  placed  in  pure 

*  Arrangement  as  iu  the  collecting  of  gases  in  the  eudiometer  tube 
(see  page  24,  and  Experiment  10  of  Laboratory  Appendix). 

1  If  the  generated  gas  is  allowed  to  escape  freely  for  a  little  wbile 
before  an  attempt  is  made  to  collect  it,  the  air  will  all  have  been  expelled 
from  tbo  apparatus  so  that  the  pure  product  will  be  obtained.  If  this 
precaution  is  not  taken,  the  inverted  tube  will,  of  course,  be  partly  filled 
with  air. 


90  ELEMENTS   OF  CHEMISTRY. 

ammonia  gas  at  ordinary  temperatures  no  appreciable 
change  takes  place.  A  different  result  is  obtained  when 
the  metals  are  heated  ;  but  as  hot  potassium  and  sodium 
are  dangerous  to  handle,  we  must  look  for  some  other 
metal  which,  while  decomposing  ammonia  as  readily  as 
the  two  just  mentioned,  will  be  easily  handled  and  safe 
for  experimentation.  Such  a  metal  is  found  in  mag- 
nesium. 

Magnesium  is  a  metal  with  a  bright  white  lustre.  When 
exposed  to  the  air  it  gradually  oxidizes.  Unlike  sodium  or  potas- 
sium, it  does  not  attack  cold  water,  liberating  hydrogen.  Mag- 
nesium is  generally  brought  into  the  market  in  the  form  of  a 
narrow  ribbon,  or  as  wire ;  the  powdered  metal  is  also  used  to  a 
considerable  extent.  When  ignited  in  the  air,  magnesium  burns 
with  a  brilliant  white  flame.  It  should  be  prevented  from  tarnish- 
ing by  being  kept  in  a  well-stopped  bottle. 

Decomposition  of  Ammonia  by  Means  of  Magnesium.  A  tube 
of  so-called  infusible  gas,  partly  filled  with  pieces  of  magnesium 
ribbon,  is  connected  at  one  end  with  an  apparatus  which  will 
generate  dry  ammonia  (Experiment  49),  and  at  the  other  end 
with  a  vessel  of  water  in  which  is  inverted  a  small  bottle  filled 
with  water.  All  air  is  first  expelled  from  the  apparatus  by  means 
of  a  slow  current  of  ammonia;  and  then,  without  interrupting  the 
current,  the  magnesium  is  gently  heated  by  means  of  an  ordinary 
burner.  The  metal  soon  becomes  coated  with  a  grayish  powdery 
crust,  while  the  gas  which  passes  on  is  collected  in  the  inverted 
flask  over  water.  When  all  the  liquid  has  been  expelled  from  the 
inverted  bottle,  the  latter  should  be  removed,  and  a  lighted  taper 
applied  to  its  mouth.  The  gas  which  has  been  collected  burns 
with  a  colorless  flame,  and  has  the  properties  which  we  have 
learned  to  associate  with  hydrogen.* 8l 

*  Ammonia  extinguishes  a  lighted  taper,  but  does  not  take  fire;  hy- 
drogen extinguishes  a  lighted  taper  which  is  plunged  into  it,  but  itself 
takes  fire  at  the  point  of  contact  with  oxygen.  Another  distinction  be- 
tween the  gas  which  is  here  collected  and  the  ammonia  from  which  it  is 
generated  is,  that  ammonia  is  very  soluble  in  water,  while  this  gas  is  not. 


COMPOUND   OF  HYDROGEN  AND   NITROGEN.     91 

The  Hydrogen  which  is  liberated  comes  from  the  Ammonia. 
We  have  already  seen  (page  23)  that  hydrogen  is  not 
formed  from  the  metals  which  act  upon  water  or  hydro- 
chloric acid,  but  that  it  owes  its  origin  to  a  decomposi- 
tion of  those  compounds,  hy  means  of  which  the  metals 
take  the  place  of  (substitute)  the  hydrogen.  It  seems, 
therefore,  scarcely  necessary  to  advance  similar  proofs 
that  the  hydrogen  generated  by  the  action  of  magnesium 
on  ammonia  does  not  come  from  the  magnesium,  but 
does  come  from  the  ammonia.  Ammonia,  therefore, 
contains  hydrogen,  which  is  liberated  from  it  by  the 
action  of  magnesium,  just  as  the  same  gas  is  generated 
by  the  action  of  metals  on  hydrogen  chloride  or  water. 
It  now  remains  to  be  ascertained  with  what  element  the 
hydrogen  in  ammonia  is  united. 

Isolation  of  the  Nitrogen  in  Ammonia.  For  this  purpose  a 
bottle  is  filled  with  a  concentrated  solution  of  common  salt,  and 
inverted  over  a  vessel  containing  the  same  fluid.  This  bottle  is 
then  completely  filled  with  chlorine  generated  as  described  in  Ex- 
periment 21  of  the  Appendix.  It  is  then  tightly  closed  with  the 
thumb,  and  transferred  to  a  vessel  containing  concentrated  ammo- 
nia solution,  in  which  it  is  placed  mouth  downward.  A  change 
immediately  sets  in,  dense  white  fumes  fill  the  flask,  the  color  of 
the  chlorine  disappears,  and  at  the  same  time  the  liquid  rises  in 
the  bottle.  When  the  reaction  is  entirely  at  an  end,  the  bottle  is 
again  closed  with  the  thumb,  and  transferred  to  a  vessel  contain- 
ing diluted  hydrochloric  acid,  in  which  it  is  opened  and  allowed 
to  stand  for  some  time.  It  can  now  be  removed  with  its  mouth 
closed,  then  placed  upright  and  opened.  The  gas  which  remains 
is  colorless  and  odorless.  A  lighted  taper  placed  in  it  is  extin- 
guished ;  in  short,  it  is  nitrogen.*  52 

*  The  chlorine  completely  decomposes  a  portion  of  the  excessive  am- 
monia, forming  hydrogen  chloride  with  the  hydrogen,  and  leaving  nitro- 
gen. The  action  of  this  not-metal  on  ammonia  is,  therefore,  the  reverse 
of  the  action  of  the  metal  (magnesium). 


92  ELEMENTS   OF  CHEMISTRY. 

Parallelism  between  Ammonia,  Hydrogen  Chloride,  and 
Water.  The  foregoing  experiments  have  clearly  demon- 
strated that  a  metal  (magnesium)  removes  the  nitrogen 
from  ammonia  and  liberates  hydrogen,  while  a  not- 
metal  (chlorine)  removes  hydrogen  and  liberates  nitro- 
gen. Ammonia,  therefore,  is  a  compound  of  nitrogen 
and  hydrogen  ;  and  its  behavior,  so  far  as  we  have  stud- 
ied it,  has  been  exactly  parallel  to  hydrogen  chloride 
and  water. 

Relative  Volumes  of  Hydrogen  and  Nitrogen  in  Ammonia. 
The  next  step  in  our  investigation  must  be  to  ascertain 
the  relative  volumes  of  hydrogen  and  of  nitrogen  in 
ammonia.  This  is  not  so  simple  an  operation  as  it  was 
with  hydrochloric  acid  or  with  water. 

In  order  to  discover  the  proportion  of  nitrogen  in  a  given  vol- 
ume of  ammonia,  we  resort  to  a  modification  of  the  experiment 
which  was  based  upon  its  decomposition  by  chlorine  (see  page  91, 
and  Experiment  52  of  the  Laboratory  Appendix).  In  place  of 
the  bottle  we  can  substitute  a  long  glass  tube,  closed  at  one  end, 
and  divided  into  three  equal  parts  by  means  of  rubber  rings.  This 
tube  is  carefully  rilled  with  pure  chlorine  by  the  same  means  that 
were  used  in  the  previous  experiment.  Then,  by  successive  im- 
mersions of  the  open  end  in  concentrated  ammonia  solution  and 
in  diluted  hydrochloric  acid,  the  isolation  of  nitrogen  can  be 
effected  as  before.*  The  tube  should  now  be  transferred  to  a  deep 
cylinder  of  pure  water,  and  lowered  therein  to  the  point  where 
the  liquid  without  and  within  occupies  the  same  level ;  f  it 

*  As  we  shall  see  in  the  next  chapter,  hydrochloric  acid  is  capable  of 
uniting  with  ammonia  to  form  a  new  compound  (ammonium  chloride). 
This  acid  is,  therefore,  removed  by  the  surplus  of  ammonia  solution  from 
the  nitrogen  which  is  left.  Afterward  the  flask  is  placed  in  diluted  hy- 
drochloric acid  to  absorb  any  excess  of  ammonia  remaining  with  the  gas 
which  has  been  separated.  Diluted  sulphuric  acid  would  accomplish  the 
same  result. 

t  The  tube  must  be  plunged  far  enough  into  the  water  so  that  the 
level  of  the  liquid  without  and  within  is  the  same,  because  by  this 


COMPOUND   OF  HYDROGEN  AND  NITROGEN.     93 

will  then  be  seen  that  the  nitrogen  which  has  been  isolated  occu-' 
pies  exactly  one-third  of  the  total  volume  of  chlorine  with  which 
we  started.53  The  logical  interpretation  of  this  result  is  as 
follows :  — 

We  have  seen  that  chlorine  unites  with  an  equal  volume  of  hy- 
drogen to  form  hydrogen  chloride  (see  page  42).  In  the  above 
experiment,  the  hydrogen  which  combined  with  chlorine  came 
from  the  ammonia ;  and  as  the  volume  of  the  chlorine  was  equal 
to  the  capacity  of  the  tube,  the  volume  of  hydrogen  which  was 
contained  in  the  decomposed  ammonia  must  also  have  been  equal 
to  the  capacity  of  the  tube.  The  nitrogen  must  have  come  from 
that  portion  of  the  ammonia  which  gave  up  its  hydrogen ;  and  as 
the  volume  of  nitrogen  remaining  is  equal  to  one-third  the  total 
volume  of  chlorine,  it  follows  that  this  quantity  of  nitrogen  must 
have  been  combined  with  a  volume  of  hydrogen  equal  to  that  of 
the  chlorine  which  filled  the  tube.  This  tube  was  divided  into 
three  equal  parts  in  the  beginning,  and  of  these  three  parts  one  is 
left  as  nitrogen,  so  that  — 

One  volume  of  nitrogen  combines  with  three  volumes 
of  hydrogen  to  form  ammonia. 

Total  Volume  of  Hydrogen  and  Nitrogen  produced  by  the 
Decomposition  of  Ammonia.  A  final  proof  of  the  volu- 
metric composition  of  ammonia  is  easily  obtained  by  the 
following  experiment :  - 

About  25  cubic  centimetres  of  ammonia  gas  are  enclosed  in  the 
eudiometer  tube  (see  page  24),  the  volume  being  accurately 
measured  and  recalculated  to  the  standard  conditions.  Electric 
sparks  are  now  passed  through  from  a  battery  with  an  induction 
coil.  These  sparks  effect  the  decomposition  of  the  ammonia  into 
nitrogen  and  hydrogen ;  and  as  this  goes  on  the  volume  of  the  gas 
will  increase  until  it  reaches  50  cubic  centimetres  (recalculated), 
at  which  point  it  becomes  stationary.  If  the  mouth  of  the  eudi- 
ometer is  now  closed  with  the  thumb,  the  tube  inverted,  and  a 

means  we  place  the  remaining  nitrogen  under  atmospheric  pressure,  as 
was  the  chlorine  with  which  we  started. 


94  ELEMENTS   OF  CHEMISTRY. 

lighted  taper  applied,  the  gas  will  burn.     This  shows  that  hydro- 
gen has  been  liberated,  the  nitrogen  being  left  uncombined.*  54 

We  have  already  seen  that  in  ammonia  three  volumes  of  hy- 
drogen are  united  with  one  volume  of  nitrogen,  but  we  have  not 
seen  what  volume  of  ammonia  is  produced  by  the  union  of  three 
volumes  of  hydrogen  with  one  of  nitrogen.  The  experiment 
which  we  are  now  considering  furnishes  this  evidence,  for  the  50 
cubic  centimetres  of  hydrogen  and  nitrogen  which  we  have  ob- 
tained by  the  decomposition  of  25  cubic  centimetres  of  ammonia 
in  the  eudiometer  tube  must  contain  — 

3  X  12.5  cubic  centimetres  of  hydrogen  =  37.5  cubic  centimetres. 

12.5  cubic  centimetres  of  nitrogen  =  12.5  cubic  centimetres. 

The  total  =  50     cubic  centimetres. 

These  50  cubic  centimetres  of  the  mixed  gases  are,  however, 
obtained  by  the  breaking  down  of  — 

2  x  12.5  cubic  centimetres  of  ammonia  =  25     cubic  centimetres. 

If  we  reduce  all  the  above  figures  to  simple  numbers  by  dividing 
by  12.5  we  have  as  a  result  — 

Two  cubic  centimetres  of  ammonia  produce  three 
cubic  centimetres  of  hydrogen  and  one  cubic  centi- 
metre of  nitrogen ;  or,  in  general  terms,  two  volumes 
of  ammonia  are  decomposed  to  form  three  volumes  of 
hydrogen  and  one  volume  of  nitrogen.  Of  course  the 
reverse,  that  two  volumes  of  ammonia  are  formed  from 
three  volumes  of  hydrogen  and  one  of  nitrogen,  must 
also  be  true. 

Comparison  of  the  Volumetric  Composition  of  Hydrogen  Chlo- 
ride, Water,  and  Ammonia.  If  what  we  have  just  learned 
be  compared  with  the  results  obtained  with  hydrogen 

*  Nitrogen  does  not  combine  with  mercury  under  the  above  circum- 
stances, as  might  be  supposed  from  the  action  of  ammonia  on  magne- 
sium. This  can  easily  be  shown  by  enclosing  some  nitrogen  in  the  eudi- 
ometer tube  and  passing  electric  sparks  through  the  gas,  according  to 
the  method  shown  above.  The  volume  of  gas  will  not  be  altered  by  this 
means. 


COMPOUND   OF  IIYDUOGEN  AND   NITROGEN.     95 

chloride  and  water,  we  shall  discover  the  following 
remarkable  regularity :  - 

One  volume  of  hydrogen  combines  with  one  volume 
of  chlorine  to  form  two  volumes  of  hydrogen  chloride. 

Two  volumes  of  hydrogen  combine  with  one  volume 
of  oxygen  to  form  two  volumes  of  water  vapor. 

Three  volumes  of  hydrogen  combine  with  one  volume 
of  nitrogen  to  form  two  volumes  of  ammonia. 

Definite  Composition  of  Ammonia.  As  a  result  of  our 
investigations  with  ammonia,  we  have  seen  that  this 
substance,  like  all  of  the  chemical  compounds  which  we 
have  encountered,  has  a  definite  composition.  (See  page 
55.)  The  specific  gravity  of  nitrogen  is  14  if  hydro- 
gen =  1 ;  or,  in  other  words,  if  a  volume  of  nitrogen 
weighs  14  grams,  the  same  volume  of  hydrogen  weighs 
one  gram.  Three  volumes  of  hydrogen  (the  amount 
necessary  to  form  ammonia  with  one  volume  of  nitro- 
gen) would,  therefore,  weigh  three  grams,  so  that  — 

Fourteen  parts  by  weight  of  nitrogen  combine  with 
three  parts  by  weight  of  hydrogen  to  form  seventeen 
parts  by  weight  of  amomnia. 

Changes  of  Energy  attending  the  Decomposition  and  For- 
mation of  Ammonia.  In  order  to  decompose  ammonia 
into  hydrogen  and  nitrogen,  it  was  necessary  for  us  to 
add  energy.  But  it  is  evident,  from  the  ease  with 
which  this  decomposition  was  accomplished  by  means 
of  the  electric  spark,  that  the  amount  of  energy  re- 
quired for  a  quantity  of  ammonia  containing  a  given 
weight  of  hydrogen  is  not  as  great  as  in  the  case  of  an 
equivalent  amount  of  hydrogen  chloride  or  water.  In 
chemical  language,  ammonia  is  less  stable  than  the  lat- 


96  ELEMENTS   OF  CHEMISTRY. 

ter  two  substances.  Although  it  is  not  practically  pos- 
sible to  cause  nitrogen  and  hydrogen  to  unite  directly, 
these  elements  must  possess  chemical  energy  when  in 
contact;  for  the  compound  which  they  form  cannot 
afterward  be  decomposed  without  the  addition  of 
energy. 

Decomposition  of  Ammonia  and  of  Water  by  Chlorine. 
Reviewing  the  experience  gained  in  the  study  of  the 
three  hydrogen  compounds  investigated,*  we  find  that 
chlorine  will  easily  decompose  ammonia,  forming  hy- 
drogen chloride  and  nitrogen,  and  that  the  same  ele- 
ment decomposes  water  quite  slowly,  and  in  the  sunlight 
producing  hydrochloric  acid  and  oxygen.  This  shows 
us  that  chlorine  and  ammonia,  and  chlorine  and  water, 
when  in  contact,  possess  chemical  energy,  which  is  con- 
verted into  kinetic  energy  by  the  change  into  hydro- 
chloric acid  and  nitrogen,  and  into  hydrochloric  acid 
and  oxygen.  The  tendency  in  these  reactions,  as  in 
the  previous  ones  which  we  have  studied,  is  toward  a 
state  of  more  stable  equilibrium  ;  the  chlorine  and  water, 
or  the  chlorine  and  ammonia,  having  more  chemical 
energy  than  the  resulting  substances.  In  these  cases, 
therefore,  as  in  the  others,  energy  is  degraded.  (See 
pages  76  and  77.) 

Decomposition  of  Ammonia  by  Oxygen.  Ammonia  is 
also  decomposed  by  oxygen  under  the  proper  condi- 
tions. A  mixture  of  ammonia  gas  and  oxygen  will 
combine  with  a  weak  explosion  when  ignited.  Water 
and  nitrogen  are  formed  by  this  reaction.  It  follows 

*  Hydrogen  chloride,  water,  and  ammonia. 


COMPOUND   OF  11YDHOGEN  AND  NITROGEN.     97 

that  ammonia  and  oxygen  possess  more  chemical  energy 
than  water  and  nitrogen.50 

Summary. 

1.  It  is   not  practically  possible  to  cause   the  free 
elements,  nitrogen  and  hydrogen,  to  unite. 

2.  Ammonia  is  decomposed  by  hot  potassium,  sodium, 
or  magnesium,  while  hydrogen  is  liberated.     The  hy- 
drogen which  is  liberated  comes  from  the  ammonia. 

3.  Chlorine   easily   decomposes   ammonia,  liberating 
nitrogen  and  forming  hydrochloric  acid. 

4.  Ammonia  is  a  compound  of  hydrogen  and  nitrogen. 

5.  Three  volumes  of  hydrogen  unite  with  one  vol- 
ume of  nitrogen  to  produce  two  volumes  of  ammonia. 

6.  In  comparing  chlorine,  oxygen,  and  nitrogen,  we 
find   that  the  volumes^  of  hydrogen  which  unite  with 
one  volume  of  these  elements  to  form  their  respective 
hydrogen  compounds  are  as  1  :  2  :  3. 

7.  Ammonia  has  a  definite  composition  by  weight. 
Three  parts  by  weight  of  hydrogen  unite  with  fourteen 
parts  by  weight  of  nitrogen  to  produce  seventeen  parts 
by  weight  of  ammonia. 

8.  It    takes    energy   to   decompose   ammonia,   hence 
energy  must  be  given  off  in  its  formation. 

9.  Chlorine  decomposes  water  to  form  hydrochloric 
acid  and  oxygen,  and  it  also  decomposes  ammonia  to 
form  hydrogen  chloride  and  nitrogen. 


98  ELEMENTS   OF  CHEMISTRY. 


CHAPTER    XIV. 

THE    COMPOUNDS   OF   AMMONIA   WITH   ACIDS. 

The  Union  of  Ammonia  with  Hydrogen  Chloride.  If 
ammonia  gas  is  brought  in  contact  with  hydrogen  chlo- 
ride, a  change  immediately  sets  in,  heat  is  given  off,  and 
dense  white  clouds  of  a  solid  substance  are  produced^ 
which  soon  collects  on  the  sides  of  the  vessel  in  which 
the  reaction  has  taken  place.  If  exactly  equal  volumes 
of  ammonia  and  hydrochloric  acid  are  taken,  neither  of 
these  substances  will  remain  after  the  two  gases  are 
brought  in  contact.  This  fact  can  easily  be  proved  by 
the  following  experiment:- — 

Two  glass  tubes  of  equal  size,  with  one  end  of  each  narrowed 
down,  are  connected  at  the  narrow  ends  by  means  of  a  short 
piece  of  rubber  tubing  closed  at  the  centre  by  a  pinch-cock.  The 
two  glass  tubes  are  filled  with  mercury  and  placed  mouth  down- 
ward, side  by  side,  in  a  mercury  trough.  Fill  one  of  them  with 
pure  ammonia,  the  other  with  pure  hydrogen  chloride.  When  this 
has  been  done,  remove  the  pinch-cock  so  that  a  free  communica- 
tion is  established  between  the  two.  As  the  union  of  the  two 
gases  takes  place,  the  mercury  will  rise  in  the  tubes  until,  pro- 
vided no  air  has  been  admitted,  it  fills  both  vessels  completely, 
with  the  exception  of  the  small  space  occupied  by  the  solid 
produced  during  the  reaction.  The  ammonia  and  hydrochloric 
acid  have,  therefore,  without  a  remainder  of  either,  united  to 
form  a  solid  substance.  The  bulk  of  this  solid,  as  compared  to 
that  of  the  original  gases,  is  so  small  that  it  can  be  neglected.65 


THE  COMPOUNDS   OF  AMMONIA    WITH  ACIDS.     99 

Ammonium  Chloride.  The  solid  substance  produced 
by  the  union  of  ammonia  and  hydrogen  chloride  has 
the  appearance  of  salt,  and  in  properties  and  structure 
can  be  compared  with  potassium  chloride.  We  have 
learned  that  in  ammonia  there  are  three  volumes  of 
hydrogen  united  with  one  volume  of  nitrogen,  and 
that  in  hydrochloric  acid  there  is  one  volume  of  hy- 
drogen to  every  volume  of  chlorine.  If,  then,  we 
cause  equal  volumes  of  ammonia  and  hydrogen  chlo- 
ride to  unite,  we  shall  have  a  solid  substance  which 
for  every  volume  of  nitrogen  contains  four  volumes  of 
hydrogen  and  one  of  chlorine.  This  solid  is  termed 
ammonium  chloride. 

Resemblance  between  Potassium  Chloride  and  Ammonium 
Chloride.  We  can  separate  potassium  chloride  into  two 
substances,  —  potassium  and  chlorine.  If  we  remove 
the  chlorine  from  ammonium  chloride,  we  have  as  a 
remainder  a  compound  of  one  volume  of  nitrogen  with 
four  of  hydrogen.*  This  grouping  of  the  two  elements, 
nitrogen  and  hydrogen,  therefore,  in  the  formation  of 
ammonium  chloride,  plays  the  same  role  as  potassium 
does  in  forming  potassium  chloride.  For  potassium 
chloride  and  ammonium  chloride  closely  resemble  each 
other;  and,  as  the  chlorine  is  the  same  in  both,  the  re- 
mainder, potassium  and  ammonium,  must  have  a  simi- 
lar effect  in  determining  the  character  of  chemical 
compounds  in  which  they  occur.  The  difference  be- 
tween potassium  and  ammonium  is  that  the  former 
has  not  been  found  to  be  decomposable  into  two  or 

*  This  compound  is  probably  capable  of  only  a  very  brief  separate 
existence  under  peculiar  circumstances.  It  very  soon  breaks  down  into 
ammonia  and  hydrogen.  It  is  stable  when  united  with  chlorine  in 
ammonium  chloride. 


100  ELEMENTS   OF  CHEMISTRY. 

more  elements,  while  the  latter  has.  In  chemical  lan- 
guage, ammonium  is  termed  a  radicle  which  can  play 
the  part  of  an  element.  Such  radicles  are  quite  fre- 
quent in  chemistry,  and  they  display  the  character  of 
very  different  chemical  elements. 

If  we  represent  the  one  volume  of  nitrogen  in  a  given  amount 
of  ammonia  by  the  letter  N,  and  the  three  volumes  of  hydrogen 
by  H3,  we  can  construct  for  ammonia  a  formula,  NH3,  which  ex- 
presses this  relationship.  If  we  represent  the  volume  of  hydro- 
chloric acid  which  will  unite  with  the  above  quantity  of  ammonia 
to  form  ammonium  chloride  by  H  Cl,  then  we  can  represent  the 
change  which  takes  place  when  ammonia  and  hydrogen  chloride 
are  brought  in  contact  as  follows  :  — 

NH3  +  H  Cl  =  NH4  Cl. 

Now,  if  we  represent  the  quantity  of  potassium  which  will 
unite  with  the  amount  of  chlorine  in  the  above  volume  of  H  Cl 
by  the  letter  K  (from  the  word  kalium,  meaning  potassium),  then 
the  formula  for  this  weight  of  potassium  chloride  will  be  K  Cl, 
and  the  relationship  between  potassium  and  ammonium  chloride 
is  made  clear  as  follows  :  — 

K  Cl  (NH4)  Cl 

Potassium  chloride  Ammonium  chloride. 

Liberation  of  Ammonia  from  Ammonium  Chloride.  If 
potassium  hydroxide  (see  page  31)  is  intimately  mixed 
with  ammonium  chloride,  a  change  takes  place ;  potas- 
sium chloride  is  formed,  and  ammonia  passes  off.  Dur- 
ing this  reaction,  water  also  is  produced,  as  will  he 
evident  from  the  following :  - 

Potassium  hydroxide  (caustic  potash),  we  have  seen,  may  be 
regarded  as  water  in  which  one-half  of  the  hydrogen  has  been 
replaced  by  the  metal  potassium.  (Page  31.)  Ammonium  chlo- 
ride contains,  for  every  volume  of  nitrogen,  four  volumes  of 
hydrogen  and  one  of  chlorine.  .When  ammonium  chloride  and 
potassium,  hydroxide  are  brought  together,  ammonia  (which  con- 


THE  COMPOUNDS   OF  AMMONIA    WITH  ACIDS.    101 

tains  one  volume  of  nitrogen  to  three  of  hydrogen)  passes  off. 
One  volume  of  the  hydrogen  in  ammonium  chloride  has,  there- 
fore, been  left  behind.  In  forming  potassium  chloride,  however, 
the  potassium  parted  with  oxygen  and  one-half  as  much  hydro- 
gen as  is  necessary  to  form  water.  The  other  half,  therefore,  was 
supplied  by  the  ammonium  chloride.  The  change  will  become 
more  apparent  if  we  once  more  use  formulae  which  represent  the 
combining  volumes,  for  then  — 

NH4  Cl  +  KOII  =  NH3  4-  HOH  +  K  CL* 

Changes  of  Energy  taking  place  during  the  Decomposi- 
tion of  Ammonium  Chloride,  During  the  above  change, 
heat  is  evolved,  so  that  the  substances  at  the  right  of 
the  sign  of  equality  possess  less  chemical  energy  than 
do  those  at  the  left.  Chemical  energy  has  been  trans- 
formed into  kinetic  energy  in  passing  from  the  ammo- 
nium chloride  and  potassium  hydroxide  to  ammonia, 
water,  and  potassium  chloride. f  It  is  partly  for  this 
reason  that  the  change  takes  place  spontaneously ;  yet 
another  factor  also '  comes  into  play,  namely,  the  vola- 
tility of  ammonia.  It  is  a  matter  of  repeated  experi- 
ence that  decompositions  like  the  above  are  apt  to  be 
complete  if  a  volatile  substance  can  be  formed.  The 
reason  for  this  fact  cannot  be  entered  into  here,  for  its 
comprehension  requires  a  somewhat  extended  knowl- 

*  In  this  equation  N  represents  one  volume  of  nitrogen,  H4  four 
volumes  of  hydrogen,  Cl  one  volume  of  chlorine,  O  one  volume  of 
oxygen,  and  K  the  amount  of  potassium  which  will  replace  one  volume 
of  hydrogen  in  a  quantity  of  water  containing  one  volume  of  oxygen. 
This  may  he  clearer  if  we  substitute  the  term  cubic  centimetre  for 
volumes,  thus  — 

N  represents  one  cubic  centimetre  of  nitrogen,  etc. 

t  Ammonium  chloride  is  decomposed  not  only  by  potassium  hy- 
droxide ;  but  a  number  of  other  hydroxides,  such  as  sodium  hydroxide, 
calcium  hydroxide,  etc.,  will  accomplish  the  same  end.  Of  course  with 
sodium  hydroxide,  sodium  chloride,  and  with  calcium  hydroxide,  cal- 
cium chloride  would  be  formed. 


102  ELEMENTS   OF  CHEMISTRY. 

edge  of  chemical  phenomena.  It  is,  however,  not  out 
of  place  to  call  attention  to  another  case  Avhere  the 
volatility  of  a  compound  formed  during  a  chemical 
reaction  determines  the  completeness  of  that  reaction. 
We  saw  that  sodium  chloride  and  sulphuric  acid  pro- 
duced sodium  sulphate  and  hydrogen  chloride.  In  this 
case  hydrogen  chloride  was  the  volatile  substance.  If, 
in  either  of  the  reactions  just  referred  to,  enough  water 
is  added  to  dissolve  completely  all  the  ammonia  or  all 
the  hydrogen  chloride  which  passes  off,  then,  under 
ordinary  circumstances,  complete  decompositions  will 
not  result.  Neither  ammonia  nor  hydrogen  chloride 
would  then  be  more  volatile  than  the  water  in  which 
they  are  dissolved. 

The  decomposition  of  ammonium  chloride  by  bases  is  a  favor- 
ite method  of  preparing  ammonia  gas  for  laboratory  use.  As  a 
general  rule,  moist  calcium  hydroxide  (slaked  lime)  is  employed 
for  this  purpose.56 

Combination  of  Ammonia  with  Acids  in  General.  Ammo- 
nia combines  with  other  acids  as  well  as  with  hydrogen 
chloride,  and  in  each  case  the  ammonium  salt  of  the 
corresponding  acid  is  produced.  The  examples  which 
are  of  importance  to  us  in  this  work  are  as  follows :  — 

Ammonia  in  contact  with  nitric  acid  produces  ammonium 
nitrate. 

Ammonia  in  contact  with  nitrous  acid  produces  ammonium 
nitrite. 

Ammonia  in  contact  with  carbonic  acid  produces  ammonium 
carbonate. 

These  three  ammonium  compounds  occur  in  small  amounts  in 
the  atmosphere  and  also  in  the  soil. 

If  a  given  quantity  of  sulphuric  acid  is  brought  into  contact 
with  one-half  as  much  ammonia  as  can  possibly  be  taken  up  by 


THE  COMPOUNDS   OF  AMMONIA    WITH  ACIDS.    103 

this  acid,  the  primary  (acid)  sulphate  of  ammonium  is  formed. 
This  primary  sulphate  is  able  to  take  up  a  second  quantity  of 
ammonia,  equal  to  the  first,  so  as  to  produce  the  secondary  (neu- 
tral) ammonium  sulphate.  There  are,  therefore,  two  sulphates  of 
ammonium,  just  as  there  are  two  sulphates  of  potassium.  (See 
page  59.)  Indeed,  all  the  ammonium  compounds  greatly  resemble 
those  of  potassium.  When  brought  in  contact  with  soluble 
bases,  like  potassium,  sodium,  or  calcium  hydroxide,  all  ammonium 
salts  liberate  ammonia  exactly  as  is  the  case  with  ammonium 
chloride.57 

Changes  of  Energy  in  forming  Ammonium  Compounds. 
The  combination  of  ammonia  with  acids  to  form  ammo- 
nium compounds  is  attended  with  the  evolution  of 
heat.  The  ammonium  salts  produced,  therefore,  pos- 
sess less  chemical  energy  than  do  the  separate  ammonia 
and  acids. 

Chemical  Character  of  a  Solution  of  Ammonia  in  Water. 
The  solution  of  ammonia  in  water  acts  very  much  like 
a  solution  of  potassium  hydroxide.  It  can  neutralize 
acids  to  form  ammonium  salts,  just  as  the  latter  neutral- 
izes acids  to  form  potassium  salts.  (See  pages  48,  58.) 
For  this  reason  it  has  been  supposed  that  the  solution 
of  ammonia  in  water  is  really  ammonium  hydroxide ; 
but  as  all  direct  proof  on  this  subject  is  in  the  contrary 
direction,  we  must  conclude  that  ammonium  hydroxide 
does  not  exist.  Further,  a  belief  in  ammonium  hydrox- 
ide is  not  necessary  in  order  to  understand  why  ammo- 
nia solution  neutralizes  acids,  since  it  is  obvious  that 
ammonia  gas,  when  dissolved  in  water,  should  be  just 
as  capable  of  union  with  acids  to  form  ammonium  salts 
as  it  is  in  the  pure  state. 

Difference  between  Ammonium  and  Potassium  Salts.  One 
characteristic  sharply  distinguishes  the  ammonium  com- 


104  ELEMENTS   OF  C1IEMISTRY. 

pounds  ±rom  those  of  potassium ;  they  are  all  decom- 
posed by  heat,  while  the  ammonia  passes  off  as  such  if 
the  acid  with  which  it  was  combined  is  not  volatile. 
If  the  acid  with  which  the  ammonia  is  combined  is 
volatile,  the  ammonia  is  vaporized  with  the  acid,  so 
that  the  vapor  contains  ammonium  salts.  On  the  other 
hand,  potassium  does  not  vaporize  except  at  high  tem- 
peratures ;  so  that,  under  usual  conditions,  potassium 
salts  are  not  volatile. 

S  miim  ar  y . 

1.  A  volume  of  ammonia  is  capable  of  uniting  with 
an  equal  volume  of  hydrogen  chloride  to  form  a  salt- 
like  body  (ammonium  chloride). 

2.  In    ammonium    chloride   there    is    combined    one 
volume  of  nitrogen  with  four  of  hydrogen  and  one  of 
chlorine. 

3.  The  group  of  substances  composed  of  one  volume 
of  nitrogen  and  four  of  hydrogen  is  termed  ammonium, 
and  its  compounds  resemble  those  of  potassium. 

4.  Ammonium  chloride  is  decomposed  by  potassium 
hydroxide  to  form  potassium  chloride,  ammonia,  and 
water.     Other  pronounced  bases,  such  as  sodium  hy- 
droxide or  calcium  hydroxide  (slaked  lime),  can  also 
liberate  ammonia  from  ammonium  chloride. 

5.  Heat  is  evolved  during  these  changes.     Therefore 
the  chlorides,  the  ammonia,  and  the  water  which  are 
produced  possess  less  chemical   energy  than  the  am- 
monium chloride  and  the  base,  which  acted  on  each 
other. 

6.  Ammonia  combines  with  other  acids  as  well  as 
with  hydrogen  chloride.     With  the  acids  it  forms  am- 
monium   salts,    which    resemble    those    of    potassium. 


THE  COMPOUNDS   OF  AMMONIA    WITH  ACIDS.    105 

There    is    a   primary  and    secondary  sulphate    of   am- 
monium. 

7.  The  solution  of  ammonia  in  water  acts  like  a  base 
(potassium  hydroxide),  since  it  is  capable  of  neutraliz- 
ing acids  to  form  ammonium  salts. 

8.  By  heat,  ammonium  compounds  are  decomposed 
into   ammonia   and   the    corresponding   acid.      If   the 
ammonium  salt  was  that  of  a  volatile  acid,  the  vapors 
of  ammonia  and  of  the  acid  combine  as  soon  as  they 
become  cooler,  once  more  forming  ammonium  salts. 


106  ELEMENTS   OF  CHEMISTRY. 


CHAPTER    XV. 

THE    THEORY   WHICH    SEEKS   TO    EXPLAIN    THE 

LAWS    OF    DEFINITE    AND     MULTIPLE 

PROPORTIONS. 

The  Definite  Composition  of  Chemical  Compounds.  All 
the  chemical  compounds  which  we  have  encountered 
are  formed,  as  we  have  seen,  by  the  union  of  definitely 
related  masses  of  matter.  While  the  number  of  these 
compounds  has  not  been  great,  it  has  been  enough  to 
show  us  that  this  definite  relationship  is  not  the  result 
of  mere  chance.  The  idea  of  chance  is,  indeed,  entirely 
eliminated  if  we  extend  our  view  so  as  to  draw  upon 
the  experience  of  others  as  well  as  our  own.  We  shall 
find  that  all  the  numberless  true  chemical  compounds 
with  which  we  are  surrounded  have  this  in  common, 
-  that  they  are  formed  by  the  interaction  of  definitely 
related  quantities  of  the  elements.  So  general  has  this 
observation  been,  that  a  definite  and  unalterable  com- 
position is  regarded  as  an  essential  characteristic  of  a 
chemical  compound. 

Meaning  of  the  Term  "  Definite  Composition."  What  is 
understood,  by  definite  composition  has  already  been 
explained  in  the  preceding  chapters ;  yet  a  repeti- 
tion of  a  few  examples  taken  from  those  already 
studied  will  develop  this  meaning  with  greater  clear- 
ness. 


DEFINITE  AND  MULTIPLE  PROPORTIONS.     107 

One  volume  of  hydrogen  unites  with  an  equal  volume  of  chlo- 
rine to  produce  hydrogen  chloride.  If  more  of  either  gas  than  is 
necessary  for  this  relationship  is  present  before  union,  then  this 
excess  will  remain  uncombined  afterward.  Hydrogen  chloride 
is,  therefore,  formed  by  the  interaction  of  definitely  related  vol- 
umes of  hydrogen  and  chlorine.  A  given  volume  of  hydrogen 
must  always  have  the  same  weight  if  it  is  under  the  same  condi- 
tions, so  must  a  given  volume  of  chlorine.  The  ratio  between  the 
weights  of  equal  volumes  of  hydrogen  and  chlorine  is  as  1  :  35.5. 
Hence  one  part  by  weight  of  hydrogen  unites  with  35.5  parts  by 
weight  of  chlorine  to  form  36.5  parts  by  weight  of  hydrogen  chlo- 
ride. The  composition  by  weight  of  hydrogen  chloride  is,  there- 
fore, a  definite  one,  and  so  is  the  relationship  between  the  weights 
of  its  constituent  parts,  hydrogen  and  chlorine. 

Similar  considerations  have  shown  us  that  the  ratio  between 
the  volumes  of  hydrogen  and  oxygen,  and  hydrogen  and  nitrogen, 
which  are  united  in  watdr  and  ammonia  respectively,  is  a  definite 
one  (2  :  1  in  water  and  3  :  1  in  ammonia).  The  ratio  between  the 
weights  of  equal  volumes  of  hydrogen  and  oxygen  is  as  1  : 16,  and 
between  those  of  equal  volumes  of  hydrogen  and  nitrogen  as  1 : 14. 
Therefore  the  relationship  between  the  weights  of  hydrogen  and 
oxygen  in  water  is  a  definite  one ;  i.e.,  2:16  (2  volumes  of  hydro- 
gen, 1  volume  of  oxygen),  or  in  simpler  numbers,  1  :  8.  Similarly, 
the  relationship  between  the  weights  of  hydrogen  and  nitrogen 
in  ammonia  is  as  3  :  14  (3  volumes  hydrogen  to  1  volume  nitro- 
gen) or  1  :  4.67. 

Definite  Relationship  between  the  Weights  of  Chemically 
Interacting  Compounds.  That  a  definite  relationship  also 
exists  between  the  weights  of  chemically  interacting 
bodies  is  shown  by  the  following  examples  which  we 
have  encountered:  — 

Sodium  attacks  water  to  form  sodium  hydroxide.  Suppose 
we  take  18  grams  of  water;  i.e.,  the  amount  of  water  which  is 
produced  by  the  union  of  two  grams  of  hydrogen  with  16  of 
oxygen.  This  quantity  of  water  will  be  completely  converted 
into  sodium  hydroxide  when  exactly  one-half  the  hydrogen  (one 


108  ELEMENTS   OF  CHEMISTRY. 

gram)  has  been  expelled  by  the  sodium.  If  less  sodium  is  used, 
then  some  water  will  remain  unaffected;  if  more  sodium,  then 
some  sodium  will  remain  unchanged.  Sodium  hydroxide,  then, 
has  a  definite  composition ;  it  contains  for  every  23  parts  of 
sodium,  16  of  oxygen  and  one  of  hydrogen.  It  can  be  shown 
in  the  same  way  that  39  grams  of  potassium  always  replace  one 
gram  of  hydrogen  in  water,  so  that  potassium  hydroxide  contains 
for  every  39  parts  by  weight  of  potassium,  16  of  oxygen  and  one 
of  hydrogen. 

When  metals  are  acted  on  by  dilute  acids,  a  similar  definite 
relationship  exists  between  the  weight  of  metal  dissolved,  the 
amount  of  hydrogen  evolved,  and  the  composition  of  the  salt  pro- 
duced. Thus  hydrogen  chloride,  as  we  have  seen,  contains  35.5 
parts  of  chlorine  to  one  part  of  hydrogen.  If  36.5  grams  of 
hydrogen  chloride  are  acted  upon  by  enough  sodium  to  replace 
all  the  hydrogen,  then  23  grams  of  sodium  will  be  necessary  for 
this  decomposition.  The  sodium  chloride  which  is  produced, 
therefore,  contains  23  parts  of  sodium  to  every  35.5  parts  of 
chlorine.  If  potassium  is  used  to  act  upon  the  above  quantity 
of  hydrogen  chloride,  39  parts  of  potassium  replace  one  part  of 
hydrogen  to  produce  potassium  chloride,  which  salt  has  39  parts 
of  potassium  to  35.5  parts  of  chlorine.  Parallel  results  can  be  ob- 
tained with  other  metals  which  are  attacked  by  dilute  acids.  The 
following  table  embodies  the  results  developed  by  a  study  of  the 
action  of  a  few  of  the  metals  on  diluted  acids  and  on  water  :  — 

One  part  of  hydrogen  is  replaced  by  23  parts  of  sodium  in  its 
action  on  water. 

One  part  of  hydrogen  is  replaced  by  39  parts  of  potassium  in 
its  action  on  water. 

The  resulting  compounds  have  the  following  composition:  — 

Sodium  hydroxide  contains  23  parts  of  sodium  to  16  of  oxygen 
and  1  of  hydrogen. 

Potassium  hydroxide  contains  39  parts  of  potassium  to  16  of 
oxygen  and  1  of  hydrogen. 

One  part  of  hydrogen  is  replaced  by  23  parts  of  sodium  in  its 
action  on  hydrogen  chloride. 

One  part  of  hydrogen  is  replaced  by  39  parts  of  potassium  in 
its  action  on  hydrogen  chloride. 


DEFINITE  AND  MULTIPLE  PROPORTIONS.     109 

One  part  of  hydrogen  is  replaced  by  32.6  parts  of  zinc  in  its 
action  on  hydrogen  chloride. 

One  part  of  hydrogen  is  replaced  by  12.1  parts  of  magnesium  in 
its  action  on  hydrogen  chloride. 

One  part  of  hydrogen  is  replaced  by  28  parts  of  iron  in  its  action 
on  hydrogen  chloride. 

The  resulting  compounds  have  the  following  composition  :  — 

Sodium  chloride  contains  23  parts  of  sodium  to  35.5  parts  of 
chlorine. 

Potassium  chloride  contains  39  parts  of  potassiam  to  35.5  parts 
of  chlorine. 

Zinc  chloride  contains  32.6  parts  of  zinc  to  35.5  parts  of 
chlorine. 

Magnesium  chloride  contains  12.1  parts  of  magnesium  to  35.5 
parts  of  chlorine. 

Iron  chloride  contains  28  parts  of  iron  to  35.5  parts  of  chlorine. 

One  part  of  hydrogen  is  replaced  by  23  parts  of  sodium  in  its 
action  on  sulphuric  acid. 

One  part  of  hydrogen  is  replaced  by  39  parts  of  potassium  in  its 
action  on  sulphuric  acid. 

One  part  of  hydrogen  is  replaced  by  32.6  parts  of  zinc  in  its 
action  on  sulphuric  acid. 

One  part  of  hydrogen  is  replaced  by  12.1  parts  of  magnesium  in 
its  action  on  sulphuric  acid. 

One  part  of  hydrogen  is  replaced  by  28  parts  of  iron  in  its  action 
on  sulphuric  acid. 

The  resulting  compounds  have  the  following  composition :  — 

Sodium  sulphate  contains  23  parts  of  sodium  to  16  of  sulphur 
and  32  of  oxygen. 

Potassium  sulphate  contains  39  parts  of  potassium  to  16  of 
sulphur  and  32  of  oxygen. 

Zinc  sulphate  contains  32.6  parts  of  zinc  to  16  of  sulphur  and 
32  of  oxygen. 

Magnesium  sulphate  contains  12.1  parts  of  magnesium  to  16 
of  sulphur  and  32  of  oxygen. 

Iron  sulphate  contains  28  parts  of  iron  to  16  of  sulphur  and  32 
of  oxygen.  x 


110  ELEMENTS   OF  CHEMISTRY. 

The  Equivalent  Weights  of  the  Metals.  It  will  be  no- 
ticed, on  examining  the  above  table,  that  the  weight  of 
any  given  one  of  the  metals  which  replaces  one  part  of 
hydrogen  in  the  acids  is  the  same,  no  matter  whether  we 
use  hydrochloric  or  sulphuric  acid.  The  same  is  true 
whatever  acid  we  employ.  For  example,  23  parts  of 
sodium  always  replace  one  part  of  hydrogen  in  any 
acid.  The  relative  weights  of  the  metals  which  are 
given  above  are  termed  their  equivalent  weights,  since 
they  are  equivalent  in  combining  power  to  one  part 
of  hydrogen. .  These  equivalent  weights  can  be  easily 
determined  by  experiment.  We  have  but  to  weigh  a 
small  quantity  of  the  metal  whose  equivalent  weight  we 
wish  to  determine,  dissolve  this  in  an  acid,  and  carefully 
collect  and  measure  the  hydrogen  evolved.  Knowing 
the  weight  of  one  cubic  centimetre  of  hydrogen,*  we 
can  readily  discover  the  volume  occupied  by  one  gram, 
and,  knowing  the  weight  of  the  metal  dissolved  and  the 
number  of  cubic  centimetres  of  hydrogen  evolved,  we 
can  calculate  the  quantity  of  metal  necessary  to  give  us 
one  gram  of  hydrogen.58  The  salts  mentioned  in  the 
above  table  can  also  be  produced  by  neutralizing  the 
corresponding  acids  with  the  corresponding  hydroxides 
of  the  metals ;  but  their  composition  by  weight  remains 
unaltered,  no  matter  what  has  been  their  method  of 
formation. 

An  Explanation  of  the  Existence  of  Fixed  Relationship  by 
Weight  in  Chemical  Compounds  is  found  in  the  Atomic 
Theory.  As  the  fixed  relationship  existing  between 
the  masses  of  the  combining  elements  in  chemical 
compounds  is  not  the  result  of  mere  chance,  it  follows 

*  One  cubic  centimetre  of  hydrogen  weighs  .00009001  gram. 


DEFINITE  AND  MULTIPLE  PROPORTIONS.     Ill 

that  some  reason  may  be  found  for  this  regularity. 
Why  should  chemical  compounds  always  show  an  un- 
varying composition  by  weight?  Why  should  not 
water,  for  example,  at  one  time  contain,  for  every  one 
part  of  hydrogen,  seven  of  oxygen,  and  at  another  time 
nine  ?  The  scientific  world  has  sought  for  an  explana- 
tion of  these  conditions,  and  has  produced  a  theory 
which  satisfactorily  accounts  for  all  the  phenomena  en- 
countered. This  theory  is  known  as  the  atomic  theory. 

The  Atomic  Theory.  Let  us  suppose  that  all  of  the 
elements  are  composed  of  extremely  small  particles 
which  we  will  term  atoms.  Let  us  further  suppose 
that  the  weight  of  an  atom  of  a  given  element  is  equal 
to  that  of  each  other  atom  of  the  same  element,  but 
differs  from  that  of  an  atom  of  any  other  element. 
The  atoms  of  different  elements  unite  to  form  the 
smallest  individual  group  of  the  compound.  Atoms 
of  the  same  kind  unite  to  produce  the  smallest  indi- 
vidual group  of  an  element.  These  groups  we  term 
molecules,  and  the  agglomeration  of  molecules  forms 
tangible  matter.  To  make  the  results  of  a  theory  such 
as  this  more  apparent,  we  can  use  an  illustration  in 
which  certain  visible  portions  of  matter  will  serve  as 
atoms.  Let  us  take  two  kinds  of  shot,  one  kind  lead, 
the  other  copper,  the  lead  shot  each  to  weigh  one  gram, 
the  copper  shot  five  grams.  If,,  now,  one  of  the  lead  is 
fastened  to  one  of  the  copper,  the  resulting  combination 
will  contain  one  part  of  lead  to  five  of  copper.  Next, 
let  us  continue  this  process  of  uniting  one  lead  shot 
with  one  copper  shot  until  we  have  a  large  number  to- 
gether, say  six  hundred  grams.  It  is  obvious  that,  if  we 
separate  all  the  copper  from  all  the  lead,  we  shall  have 


112  ELEMENTS   OF  CHEMISTRY. 

five  hundred  grams  of  the  former  to  one  hundred  grams 
of  the  latter.  In  other  words,  this  large  mass  of  com- 
bined lead  and  copper  will  have  the  same  relationship 
by  weight  between  the  constituent  elements  as  is  found 
in  the  individual  shot.  Furthermore,  if  the  above  con- 
ditions have  been  carefully  adhered  to,  it  will  not  be 
possible  to  have  any  other  relationship  between  the 
copper  and  lead  than  that  of  five  to  one,  no  matter 
how  many  shot  we  take.  Obviously  it  is  not  neces- 
sary to  know  how  many  shot  we  have  in  a  given  mass 
in  order  to  ascertain  the  relative  weights  of  the  par- 
ticles of  lead  and  of  copper.  We  need  but  to  separate 
and  weigh  all  the  lead  and  all  the  copper  to  know  that 
the  proportion  of  each  is  as  one  to  five.  While  this 
last  separation  will  tell  us  what  the  proportional  parts 
by  weight  of  the  constituent  metals  in  each  of  the  com- 
bined particles  are,  it  will  not  tell  us  how  many  indi- 
vidual shot  are  united  in  each  of  these  unless  we  know 
the  weight  of  each.  If  some  one,  for  example,  had  sub- 
stituted lead  shot  weighing  half  a  gram  each  for  those 
originally  used,  and  had  attached  two  lead  shot  to  one 
of  copper,  the  results  on  separating  the  lead  from  the 
copper  would  remain  the  same,  five  parts  of  copper  to 
one  of  lead.  In  such  case  we  could  not  ascertain  the 
number  of  lead  shot  without  counting  them. 

Difficulty  of  Determining  the  Number  of  Atoms  combined 
in  a  Molecule.  It  is  in  this  latter  condition  that  chem- 
istry finds  itself.  It  can  take  large  masses  of  matter, 
separate  these  into  their  constituent  elements,  and  weigh 
the  latter.  It  can  show  that  so  many  parts  by  weight  of 
one  element  combine  with  so  many  parts  by  weight  of 
another.  It  can,  therefore,  determine  that  the  small- 


DEFINITE  AND  MULTIPLE  PROPORTIONS.     113 

est  particles  of  the  compound  (the  molecules)  contain 
so  many  parts  of  one  element  to  so  many  parts  of  an- 
other ;  but  without  some  special  means  of  counting,  it 
cannot  determine  the  number  of  atoms  of  any  of  the 
elements  which  go  to  make  up  those  smallest  particles. 
A  direct  count,  as  in  the  case  of  the  shot,  is  out  of  the 
question,  for  we  can  neither  see  nor  weigh  the  individ- 
ual atoms.  For  example,  we  have  abundant  proof  in 
the  preceding  work  that  one  part  of  hydrogen  combines 
with  eight  parts  of  oxygen  to  form  nine  parts  of  water. 
We  have  the  theory  that  hydrogen  and  oxygen  are 
formed  of  atoms,  that  one  or  more  atoms  of  hydrogen 
unite  with  one  or  more  atoms  of  oxygen  to  form  the 
smallest  particle  (the  molecule)  of  water.  We  can  say 
that  this  molecule  contains  one  part  of  hydrogen  to 
eight  of  oxygen,  but  we  cannot,  with  the  knowledge 
which  we  now  possess,  determine  how  many  atoms  of 
hydrogen  and  how  many  atoms  of  oxygen  there  are  in 
this  molecule.  As  a  consequence,  we  cannot,  using  the 
knowledge  we  have  so  fa?  obtained,  ascertain  the  rela- 
tive weights  of  these  atoms  in  this  case.  We  merely 
know  that  there  is  eight  times  as  much  oxygen  as 
hydrogen.  We  may,  at  the  very  outset,  abandon  the 
hope  of  determining  the  absolute  weights  of  the  atoms; 
for,  unlike  the  shot  which  we  used  as  an  illustration, 
they  are  too  small  to  be  weighed  directly.  What  is 
true  of  water  is  also  true  of  hydrogen  chloride,  of  am- 
monia, of  caustic  soda,  and  of  every  other  compound 
which  we  have  studied  and  found  to  be  of  definite 
composition  by  weight.  We  can  determine  the  num- 
ber of  parts  by  weight  of  each  element  which  enters 
into  these  compounds.  We  can  suppose  that  the  cause 
of  this  definite  relationship  is  to  be  found  in  the  fact 


114  ELEMENTS   OF  CHEMISTRY. 

that  these  elements  are  composed  of  atoms,  each  hav- 
ing a  definite  mass.  We  assume  that  the  combination 
of  these  atoms  produces  molecules  of  a  fixed  composi- 
tion which  belongs  also  to  the  tangible  quantities  of  the 
compounds  produced  by  heaping  together  these  mole- 
cules, but  further  than  this  we  cannot  go. 

Practical  Advantages  of  the  Atomic  Theory  as  we  have 
so  far  developed  it.  The  atomic  theory,  as  we  have  so 
far  developed  it,  has,  therefore,  no  particular  practical 
bearing  on  our  understanding  of  chemistry.  It  affords 
an  explanation  of  the  law  of  definite  proportions  (see 
page  55)  ;  but  without  it  we  can  just  as  well  go  on 
studying  chemical  reactions  and  chemical  energy,  and 
determine  the  relative  parts  by  weight  in  which  the  ele- 
ments combine.  If,  however,  we  can  find  some  method 
of  ascertaining  the  number  of  atoms  combined  in  the 
individual  molecules  of  a  large  number  of  chemical 
compounds,  we  can  ascertain  the  relative  weights  of 
the  individual  atoms.  By  "this  means,  possibly,  we 
can  make  clear  relationships  existing  between  com- 
pounds which  would  otherwise  be  concealed.  In  that 
case  the  atomic  theory  would  be  of  the  greatest  prac- 
tical importance. 

Thoroughly  scientific  means  of  ascertaining  the  num- 
ber of  atoms  united  in  the  individual  molecules  of  many 
compounds  really  have  been  established,  and  one  of  the 
methods,  the  most  important,  we  will  examine  in  the 
next  chapter.  Before  we  take  up  this  part  of  the  discus- 
sion, however,  we  must  examine  two  other  chemical  laws 
which,  while  not  absolutely  essential  in  establishing  the 
atomic  theory,  are,  nevertheless^  of  great  importance  in 
furnishing  proof  that  is  based  upon  correct  reasoning. 


DEFINITE  AND  MULTIPLE  PROPORTIONS.     115 

The  Law  of  Multiple  Proportions.  The  first  of  these 
laws  is  known  as  the  law  of  multiple  proportions.  The 
illustrations  of  this  law  which  we  have  studied  were 
found  during  the  discussions  of  the  oxides  of  sulphur 
and  of  sulphuric  acid.  (See  Chapter  IX.)  We  there 
saw  that  sulphur  is  capable  of  forming  two  oxides,  sul- 
phur dioxide  and  sulphur  trioxide,  and  the  parts  of 
oxygen  which  unite  with  one  part  of  sulphur  in  these 
two  compounds  are  to  each  other  as  1:  1.5.  If  we 
multiply  hy  two,  so  as  to  produce  whole  numbers,  we 
have  — 

Two  parts  of  sulphur  are  united  with  two  parts  of 
oxygen  in  sulphur  dioxide. 

Two  parts  of  sulphur  are  united  with  three  parts  of 
oxygen  in  sulphur  trioxide." 

This  individual  case  is  but  an  example  of  what  gen- 
eral experience  in  chemistry  has  taught  us.  Many 
elements,  like  sulphur  and  oxygen,  combine  with  each 
other  in  more  than  one  proportion,  forming  more  than 
one  compound.  In  every  instance  where  one  element 
(A)  unites  with  a  second  element  (B)  in  more  than 
one  proportion,  in  the  series  of  compounds  so  produced 
the  proportional  parts  of  B,  which  combine  with  a  given 
quantity  of  A,  are  to  each  other  in  a  simple  ratio  such 
as  1 :  2,  or  2 :  3,  or  3 :  4.  What  is  true  of  compounds 
composed  of  two  elements  is  also  true  of  those  contain- 
ing three  or  more. 

Relation  of  the  Law  of  Multiple  Proportions  to  the  Atomic 
Theory.  This  law  of  multiple  proportions  can  readily 
be  explained  by  the  atomic  theory,  as  will  be  evident  if 
we  once  more  resort  to  our  illustration  with  the  lead 
and  the  copper  shot.  We  have  a  number  of  lead  shot 


116  ELEMENTS   OF  CHEMISTRY. 

each  weighing  one  gram,  and  a  number  of  copper  shot 
each  weighing  five  grams.  If  we  fasten  one  lead  shot 
to  one  of  copper,  we  shall  have  produced  a  mass  con- 
taining one  part  of  lead  to  five  of  copper.  Now  let  us 
take  a  second  lead  shot  and  attach  it  to  two  of  copper. 
It  is  obvious  that  the  resulting  body  will  have  one  part 
of  lead  to  ten  of  copper,  and  if  we  compare  the  two 
combinations,  we  see  that  the  weight  of  the  copper 
united  to  one  part  of  lead  in  the  first,  is  to  the  weight 
of  copper  united  to  one  part  of  lead  in  the  second,  as 
1:2.  The  same  must  be  true  if  we  take  any  number  of 
individuals  of  the  first  combination  and  compare  them 
with  any  number  of  the  second.  The  proportion  be- 
tween the  weights  of  the  lead  and  copper  in  the  first 
will  always  be  as  1 :  5,  and  in  the  second  as  1 :  10 ;  and 
the  relation  between  the  weight  of  copper  united  with 
one  part  of  lead  in  the  two  will  always  be  as  1 :  2. 

We  can  explain  the  law  of  multiple  proportions  in 
the  same  way  if  we  use  the  atomic  theory  outlined  on 
page  110.  We  have  two  oxides  of  sulphur.  In  the 
first  we  have  two  parts  of  sulphur  to  two  of  oxygen, 
and  in  the  second  two  parts  of  sulphur  to  three  of 
oxygen.  Let  us  suppose  now  that  the  smallest  par- 
ticles (the  molecules)  of  the  first  oxide  are  each  formed 
of  one  atom  of  sulphur  united  to  two  atoms  of  oxygen, 
each  molecule  containing  equal  parts  by  weight  of  sul- 
phur and  oxygen.  One  atom  of  oxygen  would  then 
weigh  half  as  much  as  an  atom  of  sulphur.  Since  any 
large  mass  of  this  sulphur  oxide  would  be  formed  of 
these  molecules,  it  would  follow  that,  if  we  separated 
all  the  sulphur  from  all  the  oxygen  in  this  large  mass, 
we  should  obtain  equal  weights  of  sulphur  and  of  oxy- 
gen. Next,  let  us  return  to  the  molecule  and  add  to 


DEFINITE  AND  MULTIPLE  PEOPORTIONS.     117 

it  one  atom  of  oxygen.  This  second  molecule  would 
then  contain  two  parts  of  sulphur  to  three  of  oxygen, 
and,  obviously,  a  tangible  mass  made  up  of  these  mole- 
cules would  also  be  separable  into  two  parts  of  sulphur 
and  three  of  oxygen.  The  relationship  existing  between 
the  amounts  of  oxygen  united  to  a  given  weight  of 
sulphur  in  the  two  oxides  of  sulphur  (sulphur  dioxide 
and  sulphur  trioxide)  is  therefore  explained  by  the 
atomic  theory.  If  this  explanation  applies  to  the  two 
compounds  which  we  have  discussed,  it  must  also 
necessarily  apply  to  any  other  series  of  compounds 
which,  like  the  two  oxides  of  sulphur,  are  formed  of 
two  or  more  elements  according  to  the  law  of  multiple 
proportions. 

The  Law  of  Multiple  Proportions  cannot  help  us  to  deter- 
mine the  Relative  Weights  of  the  Atoms.  We  cannot,  how- 
ever, see  and  weigh  the  molecules  directly ;  they  are  too 
small.  We  can  only  determine  the  proportional  parts 
in  which  the  elements  unite  in  tangible  masses  of  the 
compounds.  It  follows  from  this  that  we  cannot,  by 
ascertaining  these  proportional  parts  alone,  absolutely 
fix  the  relative  weights  of  the  atoms  themselves ;  we 
can  only  say  that  they  must  be  so  united  in  the  mole- 
cules of  the  compounds  that  the  weight  of  all  the 
atoms  of  one  element  in  one  molecule  must  be  to  the 
weight  of  all  the  atoms  of  the  second  element  in  that 
molecule  as  the  weight  of  one  element  is  to  the  weight 
of  the  other  in  the  large  quantity  of  the  compound 
with  which  we  come  in  contact.  That  this  is  so  will 
be  seen  by  the  following:  — 

We  supposed  that  one  atom  of  sulphur  was  united  to  two 
atoms  of  oxygen  in  the  molecules  of  the  first  oxide  of  sulphur, 


118  ELEMENTS   OF  CHEMISTRY. 

and  that  one  atom  of  sulphur  was  united  to  three  of  oxygen  in 
those  of  the  second.  Let  us  now  change  this  hypothesis  to  read 
that  one  atom  of  sulphur  is  joined  to  four  of  oxygen  in  one  mole- 
cule of  sulphur. dioxide,  and  to  six  in  one  of  sulphur  trioxide,  one 
atom  of  oxygen  having  just  one-fourth  of  the  weight  of  one  atom 
of  sulphur.  The  latter  view  of  the  case  would  agree  with  the  ex- 
perimental results  exactly  as  well  as  the  former ;  for  if  the  mole- 
cules of  the  oxides  of  sulphur  were  constructed  in  this  way,  sulphur 
dioxide  would  have  two  parts  of  sulphur  united  to  two  of  oxygen, 
and  sulphur  trioxide  two  of  sulphur  joined  to  three  of  oxygen. 
These  facts  are  unalterable,  and  any  hypothesis  which  we  choose 
to  adopt  must  agree  with  them. 

We  must  therefore  come  to  the  conclusion  that,  while  the  re- 
lations existijig  between  the  proportional  parts  in  which  oxygen 
and  sulphur  unite  are  explainable  by  the  atomic  hypothesis,  the 
determination  of  these  proportional  parts  alone  cannot  possibly 
help  us  to  ascertain  the  relative  weights  of  the  atoms  themselves. 
The  atomic  theory,  therefore,  in  the  form  which  we  at  present 
have  it  in  this  work,  has  no  particular  bearing  on  the  systematic 
study  of  chemistry.  This  conclusion  we  have  already  reached  in 
the  law  of  definite  proportions. 

The  Equivalent  Weights  of  Elements.  One  other  series  of 
facts  in  support  of  the  atomic  theory  is  found  by  comparing  a 
number  of  the  compounds,  each  of  which  contains  the  same 
element  united  to  others,  which  latter  are  however  different  in 
each  one  of  the  series.  This  comparison  has  already  been  insti- 
tuted in  the  table  which  was. constructed  at  the  beginning  of  this 
chapter  (pages  108  and  109). 

On  consulting  this  table  we  find  that  — 

23     parts  of  sodium, 

39     parts  of  potassium, 

32.6  parts  of  zinc,  ]•  are  united  with 

12.1  parts  of  magnesium, 

28     parts  of  iron, 

16  parts  of  oxygen  and  1  of  hydrogen  in  the  hydroxides  of  the 
above  metals,  and  with  35.5  parts  of  chlorine  in  the  chlorides  of 
the  above  metals. 


DEFINITE  AND  MULTIPLE  .I*UOPOKTIONS.     119 

Furthermore,  as  we  have  seen,  8  parts  of  oxygen'  are  united 
with  one  part  of  hydrogen  in  water.  This  table  shows  us  that 
2  times  8  parts  of  oxygen  are  combined  with  23  parts  of  sodium 
in  sodium  hydroxide,  and  with  39  parts  of  potassium  in  potassium 
hydroxide.  Also  on  page  109  we  saw  that  4  times  8  parts  of 
oxygen  are  found  together  with  23  of  sodium  and  39  of  potas- 
sium in  potassium  sulphate. 

The  examples  which  have  been  cited  have  been  con- 
fined to  the  few  elements  encountered  during  the  prog- 
ress of  this  work,  but  we  should  have  arrived  at  similar 
results  had  we  used  any  other  ones  for  our  basis  of 
study.  If,  therefore,  we  define  as  the  equivalent  weight 
of  an  element  that  part  of  this  element  which  will  com- 
bine with  one  part  of  hydrogen,  or  which  will  replace 
one  part  of  hydrogen  in  a  chemical  compound  (see 
page  110),  we  shall  arrive  at  the  following  rule :  — 

All  true  chemical  compounds  are  produced  by  the 
union  of  the  equivalent  weights,  or  of  simple  multiples  or 
sub-multiples  of  the  equivalent  weights,  of  the  elements. 

The  Formation  of  Compounds  from  the  Equivalent  Weights 
of  the  Elements  is  in  accordance  with  the  Atomic  Theory. 
The  equivalent  weight  of  an  element  is,  therefore,  a 
constant  which  accompanies  it  throughout  its  combina- 
tions with  other  elements.  It  remains  while  apparently 
all  of  the  other  characteristics  of  the  element  (i.e.,  color, 
malleability,  ductility,  etc.)  have  been  lost  in  the  for- 
mation of  a  compound  differing  in  all  its  properties 
from  the  elements  of  which  it  is  composed. 

This  result  is  entirely  in  accordance  with  the  atomic  theory ; 
for,  if  the  elements  are  formed  of  atoms,  these  atoms  must  always 
retain  the  same  relative  weights,  no  matter  how  varied  are  the 
compounds  formed  by  them.  If  an  atom  of  sodium  weighs 


120  ELEMENTS   OF  CHEMISTEY. 

23  times  as  much  as  an  atom  of  hydrogen,  and  if  one  molecule 
of  water  is  acted  on  by  sodium  in  such  a  way  that  an  atom  of 
sodium  replaces  one  of  hydrogen,  then  23  parts  of  sodium  will 
take  the  place  of  one  part  of  hydrogen,  no  matter  how  large  a 
quantity  of  water  or  of  sodium  is  taken.  Furthermore,  if  one 
atom  of  potassium  weighs  39,  one  atom  of  zinc  32.6,  one  of 
iron  28,  times  as  much  as  one  of  hydrogen,  then  potassium,  zinc, 
or  iron,  must  retain  these  relative  weights,  no  matter  in  what 
compound  they  are  encountered. 

The  Relative  Weights  of  the  Atoms  are  Simple  Multiples 
or  Sub-multiples  of  the  Equivalent  Weights.  At  first 
glance  it  would  seem  that  the  equivalent  weights 
might  be  considered  as  the  relative  weights  of  the 
atoms  themselves,  but  a  little  reflection  will  show  us 
that  such  a  conclusion  would  be  arbitrary  and  without 
warrant.  In  the  above  paragraph,  for  example,  we  have 
assumed  that  one  atom  of  sodium  replaces  one  atom 
of  hydrogen  in  water.  If  this  were  true,  the  relative 
weights  of  the  atoms  of  hydrogen  and  of  sodium  would 
be  the  same  as  the  equivalent  weights;  namely,  1  and 
23.  With  equal  right  we  might  suppose,  however, 
that  two  atoms  of  hydrogen  are  replaced  by  one  of 
sodium,  in  which  case  the  relative  weights  of  the 
atoms  of  hydrogen  and  sodium  would  be  1  and  46, 
and  the  same  considerations  would  show  us  that  the 
relative  atomic  weights  of  iron  and  hydrogen  might  be 
1  and  28,  or  1  and  56,  etc.  The  equivalent  weights 
of  the  various  elements  may  possibly  represent  the  rela- 
tive weights  of  the  atoms  themselves,  but  they  may 
also  be  some  simple  multiple  or  sub-multiple  of  those 
atomic  weights.  While  the  fact  that  all  true  chemical 
compounds  are  produced  by  the  union  of  the  equiva- 
lent weights,  or  of  simple  multiples  or  sub-multiples  of 
the  equivalent  weights  of  the  elements,  is  an  added 


DEFINITE  AND   MULTIPLE  PROPORTIONS.      121 

support  to  the  atomic  theory,  the  determination  of 
these  equivalent  weights  does  not,  without  further  ex- 
perimental aid,  help  us  to  decide  upon  the  true  relative 
weights  of  the  atoms  themselves. 

After  a  consideration  of  all  the  arguments  which  have 
been  advanced,  the  question  naturally  presents  itself: 
Are  no  experimental  means  at  our  disposal  which  will 
enable  us  to  determine  the  relative  weights  of  the 
atoms?  Must  the  atomic  theory  always  be  to  us  sim- 
ply an  explanation  of  the  reason  why  certain  regulari- 
ties in  the  composition  of  chemical  compounds  are 
encountered,  without  having  any  practical  bearing  in 
ascertaining  the  number  of  atoms  which  are  combined 
in  the  chemical  compounds,  or  the  relative  weights  of 
the  atoms  themselves?  An  attempt  to  answer  these 
questions  involves  a  more  minute  consideration  of  the 
laws  underlying  the  combining  volumes  of  gases,  and 
is,  therefore,  reserved  for  a  separate  chapter. 

Summary. 

1.  All  chemical  compounds  are  formed  by  the  union 
of  definitely  related  masses  of  matter. 

2.  A    definite    relationship  also  exists  between  the 
weights  of  chemically  interacting  bodies. 

3.  The  quantity  of  any  metal  which  is  capable  of 
liberating  one  part  of  hydrogen  from  acids  is  termed  the 
equivalent  weight  of  that  metal.     A  given  weight  of  a 
metal  when  acted  upon  by  certain  dilute  acids  always 
liberates  the  same  quantity  of  hydrogen. 

4.  The  salts  formed  by  the  substitution  of  hydrogen 
in  acids  have  a  definite  composition  by  weight.     This 
composition  is  constant,  no  matter  what  is  the  method 
of  their  formation. 


122  ELEMENTS   OF  CHEMISTRY. 

5.  The  fixed  relationship  existing  between  the  com- 
bining weights  of  the  elements  is  explainable  by  means 
of  the  atomic  theory. 

6.  The  atomic  theory  supposes  that  all  the  elements 
are  made  up  of  extremely  small  particles  termed  atoms. 
The  weight  of  an  atom  of  a  given  element  is  equal  to 
that  of  each  other  atom  of  the  same  element,  but  differs 
from  that  of  an  atom  of  any  other  element. 

7.  The  atoms  of  different  elements  unite  to  form  the 
smallest  individual  group  of  a  compound.     This  group 
is  termed  a  molecule. 

8.  While  the  fact  that  a  given  chemical  compound 
always  has  a  definite    composition    is    explainable    by 
means  of  the  atomic  hypothesis,  the  discovery  of  the 
relative  weights  of  the  different  elements  which  form 
that  compound   cannot   determine   for  us   the  relative 
weights  of  the  atoms  themselves. 

9.  Chemical  compounds  are  produced  by  the  union 
of  the  equivalent,  or  of  simple  multiples  or  sub-multi- 
ples of  the  equivalent,  weights  of  the  elements. 


MODERN   THEORY  OF  NATURE  OF  GASES.     123 


CHAPTER   XVI. 

MODERN  THEORY  OF  THE  NATURE  OF  GASES. 

The  Relation  between  Specific  Gravities  of  Gases  and  their 
Molecular  Weights. 

A  CONSIDERATION  of  the  relative  parts  by  weight  in 
which  the  atoms  unite  cannot  provide  us  with  a  satis- 
factory means  of  determining  the  relative  weights  of 
the  atoms  themselves.  But  a  combination  of  the  com- 
bining weights  with  the  combining  volumes  and  with 
the  specific  gravities  of  the  gaseous  elements  and  com- 
pounds furnishes  us  with  a  means  of  deciding  what 
multiples  or  sub-multiples  of  those  combining  weights 
we  must  regard  as  representing  .the  true  relative  weights 
of  the  atoms.  In  order  to  comprehend  how  this  com- 
bination of  the  three  constants  (combining  weights, 
combining  volumes,  and  specific  gravities  of  gaseous 
elements  and  compounds)  has  led  to  the  desired  result, 
we  must  first  understand  the  prevailing  belief  as  to  the 
physical  nature  of  a  gas.  This  prevailing  belief  is  in 
accordance  with  the  atomic  theory. 

The  Kinetic  Gas  Theory.  A  gas  is  at  the  present 
time  regarded  as  a  form  of  matter,  the  individual 
particles  of  which  (molecules)  are  so  far  separated 
that  each  is  capable  of  motion  independently  of  the 
others. 


124  ELEMENTS   OF  CHEMISTRY. 

That  the  particles  of  a  gas  must  be  comparatively  far  apart  is 
proven  by  the  fact  that  they  occupy  a  space  many  hundred  times 
greater  than  that  of  the  liquids  from  which  they  are  formed  by 
heating.  These  particles  are  at  such  a  distance  from  each  other 
that  they  are  not  subject  to  those  mutual  influences  (cohesion, 
etc.)  which  are  present  in  liquids  and  solids.  They  are,  therefore, 
acted  upon  only  by  the  attraction  which  all  masses  exert  on  each 
other  at  a  distance  (gravitation).  As  a  consequence,  the  individ- 
ual molecules  attract  each  other  only  in  a  very  slight  degree. 
Accordingly,  the  small  particles  of  which  a  gas  is  composed  are 
continually  in  motion,  and,  following  the  ordinary  laws  of  me- 
chanics, move  in  right  lines  until  they  collide  with  some  other 
molecule  of  their  own  kind,  or  with  the  walls  of  the  enclosing 
vessel,  when,  being  perfectly  elastic,  they  rebound.  The  pres- 
sure exerted  by  a  gas  is,  therefore,  due  to  the  continual  impacts 
given  by  its  molecules  upon  the  sides  of  the  retainer.  This  pres- 
sure must  consequently  increase  with  the  number  of  molecules 
and  with  the  mass  and  velocity  of  each  molecule.  The  energy 
possessed  by  a  moving  body  is  measured  by  its  mass  multiplied 
by  the  square  of  its  velocity  and  divided  by  two  (— ).  Therefore, 

if  we  multiply  the  mass  of  each  individual  molecule  in  a  given 
volume  of  the  gas  by  one-half  the  square  of  its  velocity,  we  shall 
obtain  the  energy  of  motion  possessed  by  that  molecule  ;  and  the 
sum  of  all  these  products  will,  obviously,  be  a  quantity  propor- 
tional to  the  pressure  of  the  gas.  In  discussing  the  atmosphere, 
we  learned  that  gases  expand  yfj  of  their  volume  for  each  rise 
of  one  degree  in  temperature  (law  of  Gay  Lussac,  see  page  69). 
However,  if  the  volume  of  the  gas  be  kept  constant  while  the 
temperature  is  raised,  then  the  increase  of  the  pressure  of  the  gas 
is  found  to  be  proportional  to  the  increase  in  the  temperature  (the 
latter  being  calculated  from  —273°).  In  this  velume  of  gas  the 
mass  remains  constant,  so  that  it  follows  that  the  temperature  is 
proportional  to  the  square  of  the  velocity  of  the  molecules. 

Let  us  suppose  that  we  have  two  equal  spaces,  each  filled  with 
a  different  gas,  under  the  same  temperature  and  pressure.  From 
what  has  been  said  ab^ve,  the  sum  of  the  kinetic  energy  pos- 
sessed by  the  particles  in  one  of  the  gases  will  be  equal  to  the 
sum  in  the  other.  We  will  assume  that  in  these  equal  gas  volumes 


MODERN  THEORY  OF  THE  NATURE  OF  GASES.  125 

there  are  equal  numbers  of  molecules  (hypothesis  of  Avogadro).  It 
will  follow  that  the  kinetic  energy  (-5*)  belonging  to  each  indi- 
vidual particle  in  either  of  the  gases  averages  the  same.  If 
both  gas  volumes  are  brought  into  communication,  they  will  mix 
without  suffering  either  a  change  in  temperature  or  pressure,  pro- 
vided always  that  they  exert  no  chemical  action  on  each  other. 
In  the  mixture  so  produced,  therefore,  there  is  also  on  the  average 
the  same  amount  of  kinetic  energy  belonging  to  each  individual 
molecule. 

In  Equal  Volumes  of  Gases,  under  like  Conditions,  there  are 
Equal  Numbers  of  Molecules.  Assuming  that  in  equal  vol- 
umes of  gases,  under  the  same  temperature  and  pressure, 
there  are  equal  numbers  of  molecules,  if  we  take  into 
consideration  only  the  simple  laws  of  mechanics,  we 
can  understand  why  two  gases  can  be  mixed  without 
a  change  in  temperature  or  total  volume.  We  can  also 
find  a  reason  for  like  changes  in  volume  caused  by  like 
changes  in  temperature  (law  of  Gay  Lussac),  and  for 
the  fact  that  all  gases  expand  alike  and  are  altered  alike 
in  volume  by  like  changes  in  pressure  (law  of  Boyle, 
see  page  68). 

The  matter  assumes  an  entirely  different  aspect,  however,  if 
we  do  not  assume  that  in  equal  volumes  of  gases  there  are  equal 
numbers  of  particles  under  like  conditions  of  temperature  and 
pressure.  For  example,  suppose  that  one  of  the  above  gas  volumes 
contains  twice  as  many  molecules  as  the  other.  Then,  since  the 
pressure  exerted  by  both  gases  is  alike,  and  the  sum  of  the  kinetic 
energy  of  all  the  particles  in  the  one  must  be  equal  to  that  sum 
in  the  other,  each  of  these  particles  will  possess  only  one-half  the 
kinetic  energy  which  belongs  to  a  particle*  of  the  other  gas.  It 
would  then  be  difficult  to  understand  how  the  equality  of  temper- 
ature and  pressure  could  be  preserved  after  the  two  gases  are 
mixed.  For  we  should  have  in  this  mixture  particles  possessing 
twice  as  much  kinetic  energy  as  others,  and  we  could  see  no 


126  ELEMENTS   OF  CHEMISTRY. 

reason  why,  owing  to  frequent  collisions,  these  should  not  impart 
some  of  their  energy  to  those  with  which  they  come  in  contact. 
If  this  were  to  occur,  however,  we  could  scarcely  maintain  the 
former  equality  of  temperature  and  pressure,  since  both  of  these 
are  proportional  to  the  kinetic  energy  possessed  by  the  molecules. 
Avogadro's  hypothesis,  that  in  equal  volumes  of  gases  there  are 
equal  numbers  of  molecules,  is,  therefore,  the  only  one  in  accord- 
ance with  the  laws  of  mechanics.  With  the  establishment  of  this 
hypothesis  we  have  a  method  of  determining  the  relative  weights 
of  the  molecules  of  gaseous  substances. 

The  weight  of  a  given  volume  of  gas  is  obviously  the 
sum  of  the  weights  of  the  molecules  of  which  it  is  com- 
posed. If,  now,  we  weigh  equal  volumes  of  a  series  of 
different  gases,  all  under  the  same  conditions  as  to  the 
temperature  and  pressure,  the  weights  so  obtained  will 
have  the  same  relationship  to  each  other  as  do  the 
weights  of  the  individual  molecules,  because  in  equal 
volumes  of  gases  there  are  equal  numbers  of  the  latter. 

Relation  between  the  Molecular  Weights  and  Specific  Gravities  of 
Gases.  Let  us  suppose  that  we  have  equal  volumes  of  two  gases, 
the  molecules  of  which  weigh  x  and  y  respectively.  If  the  num- 
ber of  molecules  in  the  first  volume  is  n,  then  the  number  in 
the  second  will  also  be  n,  and  — 

nx  :  ny  :  :  x  :  y 

but  nx  and  ny  represent  the  weights  of  the  two  gases  *  (w  and  w'), 
so  that  — 

w  :  w ' :  :  x  :  y. 

The  weights  of  equal  volumes  of  various  gases,  when  compared 
with  the  weight  of  an  equal  volume  of  some  other  gas  taken  as 
a  standard,  represent  the  specific  gravities  of  those  gases.  From 
what  has  gone  before,  we  can  establish  the  following  rule  :  — 

*  If  all  of  the  molecules  of  a  given.gas  volume  are  of  the  same  kind, 
then  the  sum  of  the  weights  of  the  individual  molecules  can  he  repre- 
sented as  a  product,  where  n  represents  the  number  of  molecules. 


Ill  +  litres 


MODERN   THEORY  OF  THE  NATURE  OF  GASES.     127 

The  molecular  weights  (the  relative  weights  of  the 
individual  molecules)  of  gases  are  to  each  other  as  the 
specific  gravities  of  those  gases. 

Standard  for  Specific  Gravities  of  Gases.  It  is  generally  cus- 
tomary to  compare  all  specific  gravities  of  gases  with  that  of  air 
as  unity ;  i.e.,  to  weigh  gas  volumes  which  are  equal  to  that  occu- 
pied by  one  gram  of  air.  For  our  purpose,  however,  it  will  be 
better  to  use  hydrogen  as  a  standard,  and  to  understand  by  the 
term  specific  gravity  of  a  gas,  the  relative  weights  of  volumes 
equal  to  the  space  occupied  by  the  unit  weight  of  hydrogen. 

EXAMPLES  :  —  One  gram  of  hydrogen  occupies  11 
at  0°  and  760mm.  pressure. 

11.111  +  litres«of  oxygen  weigh  16  grams, 

11.111  +  litres  of  chlorine  weigh  35.5  grams, 

11.111  +  litres  of  nitrogen  weigh  14  grams, 

11.111  +  litres  of  hydrogen  chloride  weigh  18.25  grams, 

11.111  +  litres  of  water  weigh  9  grams, 

11.111  +  litres  of  ammonia  weigh  8.5  grams, 

and  the  specific  gravities  are  as  follows  :  — 

Hydrogen  =    1. 

Oxygen  =  16. 

Chlorine  =  35.5. 

Nitrogen  =  14. 
Hydrogen  chloride  =  18.25. 

Water  =    9. 

Ammonia  =    8.5. 

These  specific  gravities,  as  we  have  seen,  bear  the 
same  relationship  to  each  other  as  do  the  molecular 
weights  of  the  respective  gases.  We  need  then  but  to 
decide  upon  the  molecular  weight  of  one  of  them  in  order 
to  have  given  to  us  the  relative  molecular  weights  of  all  of 
the  others.  Such  a  decision  has  been  reached,  and  the 
reasons  which  have  led  to  it  will  be  outlined  in.  the 
next  chapter. 


128  ELEMENTS   OF  CHEMISTRY. 

Summary. 

1.  The  individual  particles  (molecules)  of  a  gas  are 
so  far  separated  that  each  is  capable  of  motion  inde- 
pendently of  the  others. 

2.  The  pressure  exerted  by  a  gas  is  due  to  the  im- 
pacts of  its  molecules  upon  the  sides  of  the  container. 

3.  The  sum  of  the  kinetic  energy  of  all  the  mole- 
cules is  proportional  to  the  gas  pressure. 

4.  In  equal  volumes  of  gases,  under  the  same  con- 
Editions   of  temperature  and  pressure,  there  are   equal 
J  numbers  of  molecules. 

\      5.    The  weights  of  equal  volumes  of  gases  are  to  each 
other  as  the  molecular  weights. 

6.  The  molecular  weights  are  to  each  other  as  the 
specific  gravities. 

7.  The  specific  gravities  of  gases  are  usually  ascer- 
tained with  air  as  a  unity.     In  our  chemical  work  it  is 
better  to  select  hydrogen  as  the  standard. 

8.  If  we  decide  upon  the  molecular  weight  of  one 
gas,  we  can,  by  determining  their  specific  gravities,  dis- 
cover the  molecular  weights  of  other  gases. 


DETERMINATION  OF  ATOMIC   WEIGHTS.       129 


CHAPTER   XVII. 

THE   DETERMINATION   OF  ATOMIC   WEIGHTS  BY 
USE   OF   THE    SPECIFIC   GRAVITIES   OF   GASES. 

IN  the  preceding  chapter  we  learned  that,  because 
equal  volumes  of  gases  contain  equal  numbers  of  mole- 
cules, the  relative  weights  of  equal  volumes  of  gases  must 
bear  the  same  relationship  to  each  other  as  the  molec- 
ular weights.  The  determination  of  various  molecular 
weights,  therefore,  becomes  a  comparatively  easy  mat- 
ter, provided  we  can  determine  the  molecular  weight  of 
some  one  element  which  we  can  select  as  a  standard, 
and  with  which  we  can  compare  the  other  gaseous  sub- 
stances. In  order  to  do  this  we  must  examine  more 
closely  into  the  lessons  taught  us  by  the  study  of  the 
combining  volumes  of  elementary  gases. 

The  Molecules  of  Hydrogen  consist  of  Two  Atoms.     One 

volume  of  hydrogen  unites  with  one  volume  of  chlorine 
to  produce  two  volumes  of  hydrogen  chloride.  Let  us 
now  suppose  that  we  have  a  volume  of  hydrogen  which 
contains  one  hundred  molecules.  From  what  we  have 
learned,  it  follows  that  an  equal  volume  of  chlorine  also 
contains  one  hundred  molecules.  These  gas  volumes 
we  will  represent  by  squares,  as  follows :  — 


1  volume  hydrogen.    1  volume  chlorine. 


130 


ELEMENTS   OF  CHEMISTRY. 


The  above  volumes  of  hydrogen  and  chlorine  are  capa- 
ble of  uniting  to  form  a  quantity  of  hydrogen  chloride 
equal  to  twice  the  volume  of  hydrogen :  - 


1  VOL. 
HYDROGEN 

+ 

1  VOL. 
CHLORINE 

= 

2  volumes  of  hydrogen  chloride. 

Now,  each  volume  of  hydrogen  chloride  must  contain  as 
many  molecules  as  an  equal  volume  of  hydrogen  or  of 
chlorine;  i.e.,  100  molecules,  so  that  — 


100  MOLS. 

100  MOLS. 

100  MOLS. 

100  MOLS. 

OF 

HYDROGEN 

+ 

OF 

CHLORINE 

HYDROGEN 
CHLORIDE 

+ 

HYDROGEN 
CHLORIDE 

It  follows  from  this,  however,  that  100  molecules  of 
hydrogen  must  have  taken  part  in  the  formation  of  200 
molecules  of  hydrogen  chloride,  so  that  each  molecule 
of  hydrogen  must  have  been  divided  into  two  parts.  The 
molecule  of  hydrogen  thus  contains  at  least  two  atoms. 
The  same  of  necessity  must  be  true  also  of  chlorine,  for 
the  100  molecules  of  chlorine  have  also  taken  part  in 
the  formation  of  200  molecules  of  hydrogen  chloride. 
What  is  true  of  the  above  gas  volumes  is  obviously 
true  of  any  other  equal  volumes  of  hydrogen  and  chlo- 
rine, for  in  equal  volumes  there  are  equal  numbers  of 
molecules.  The  above  reasoning  does  not  exclude  a 
theory  that  a  molecule  of  hydrogen  may  contain  more 
than  two  atoms ;  but  such  a  view  has  no  great  proba- 
bility, because  in  the  formation  of  the  various  hydrogen 
compounds  we  encounter  no  instance  in  which  one 
volume  of  hydrogen  enters  into  the  production  of  more 
than  two  volumes  of  the  compound  gas. 


DETERMINATION   OF  ATOMIC   WEIGHTS.        131 

EXAMPLES  :  —  Two  volumes  of  hydrogen  and  one  of  oxygen 
produce  two  volumes  of  water  vapor. 

Three  volumes  of  hydrogen  and  one  of  nitrogen  produce  two 
volumes  of  ammonia. 

The  Molecular  Weight  of  Hydrogen  can  be  taken  as  the 
Standard  for  Measuring  other  Molecular  Weights.  It  seems 
reasonably  certain,  therefore,  that  one  molecule  of  hy- 
drogen is  formed  of  two  atoms.  Its  molecular  weight, 
then,  is  twice  its  atomic  weight.  We  have  no  accurate 
means  of  determining  the  absolute  weights  of  the  atoms, 
but  for  our  purposes  this  is  not  necessary.  The  relative 
weights  answer  all  purposes ;  and  we  need  only  select 
the  weight  of  an  atom  of  some  one  element  as  a  stand- 
ard, and  measure  all  others  by  this.*  Hydrogen  is, 
relatively,  the  lightest  of  known  elements. 

It  is  convenient,  therefore,  to  fix  upon  the  weight 
of  an  atom  of  hydrogen  as  unity,  and  to  say  that  other 
atoms  weigh  16,  14,  35.5,  etc.,  times  as  much  as  one 
atom  of  hydrogen.  If  the  atom  of  hydrogen  weighs 

1,  then  the  molecule  of  hydrogen  weighs  2. 

\ 

Determination  of  the  Molecular  Weights  of  Gases.  We 
are  now  in  a  position  to  determine  the  relative  molecu- 
lar weights  of  other  gaseous  elements  and  compounds ; 
for  we  need  but  select  a  volume  of  hydrogen  which 
weighs  two  grams,  and  then  weigh  off  volumes  of  the 
other  gases  equal  to  that  volume  of  hydrogen.  Their 
relative  weights  will  represent  the  relative  weights  of 
the  molecules. 

*  The  object  of  measuring  anything  is  simply  to  determine  its  relation 
to  other  things.  We  fix  upon  some  arbitrary  standard  (a  foot,  a  metre,, 
an  inch)  as  a  unit,  and  measure  all  other  lengths  by  this.  The  same  is 
true  of  weights —  the  unit  of  weight  (a  grain,  a  gram,  a  kilogram)  is  one 
of  arbitrary  selection. 


132 


ELEMENTS   OF  CHEMISTRY. 


If  n  represents  the  number  of  molecules  in  2  grams  of  hydrogen, 
then  -  will  be  the  weight  of  each  individual  molecule.  If  x,  y,  z 
represent  the  weights  of  volumes  of  other  gases  equal  to  that  of 
2  grams  hydrogen,  then  -,  ^,  -,  will  be  the  relative  weights  of 
the  individual  molecules  of  each  of  those  gases,  since  n  remains 
the  same  ;  and  2  :  x  :  y  :  z  :  :  - :  - :  V- :  - '-.  Hence,  if  2  represents  the 
weight  of  one  molecule  of  hydrogen,  the  relative  weights  of  the 
other  molecules  are  represented  by  x,  y,  and  z ;  i.e.,  by  their  specific 
gravities.  Obviously  the  same  result  will  be  obtained  if  we  begin, 
not  with  two  grams  of  hydrogen,  but  with  two  units  of  any  other 
standard  of  weight,  so  that  we  can  establish  the  following  rule  :  — 

If  hydrogen  is  placed  at  2,  the  specific  gravities  of  all 
other  gases  (which  are  measured  by  these  two  parts  of  hy- 
drogen) are  the  same  numbers  as  their  molecular  weights. 
This  rule  is  illustrated  by  the  following  table :  - 

Hydrogen  =  2. 


GAS. 

SPECIFIC 
GRAVITY. 

MOLECULAR 
WEIGHT. 

Chlorine    

71. 

71. 

Oxv^en 

32. 

32. 

Nitrogen  

28. 

28. 

Hydrogen  chloride      .     .     . 
Water  (gas)       
Ammonia 

36.5 
18. 
17. 

36.5 

18. 
17. 

Determination  of  the  Maximum  Atomic  Weights  of 
the  Elements.  By  means  of  these  results  we  obtain  a 
method  for  determining  the  maximum  numbers  which 
can  represent  the  relative  weights  of  the  atoms  of  chlo- 
rine, oxygen,  and  nitrogen.  This  conclusion  is  evident 
if  we  analyze  the  figures  a  little  more  closely. 

-  The  weight  of  a  molecule  of  water  is  18  if  the  molecule  of 
hydrogen  is  2.  Our  previous  work  has  shown  us  that  in  18  parts 
of  water  there  are  16  of  oxygen  and  two  of  hydrogen.  Hence 


DETERMINATION  OF  ATOMIC    WEIGHTS.        133 

one  molecule  of  water  contains  16  parts  of  oxygen  and  two  of 
hydrogen.  Obviously,  then,  one  atom  of  oxygen  cannot  weigh 
more  than  16  times  as  much  as  one  atom  of  hydrogen ;  for,  if  its 
relative  weight  were  supposed  to  be  greater  than  this,  one  mole- 
cule of  water  would  contain  a  fraction  of  one  atom  of  oxygen. 
We  cannot  with  equal  certainty  state  that  an  atom  of  oxygen  may 
not  have  a  relative  weight  of  less  than  16,  for  it  is  easily  conceiv- 
able that  a  molecule  of  water  may  contain  more  than  one  atom  of 
oxygen.  Such  a  supposition,  however,  would  be  entirely  without 
experimental  backing.  We  have  never  encountered  any  one  of 
the  numerous  compounds  of  oxygen  (which  we  can  obtain  as 
gases,  and  the  molecular  weights  of  which  we  consequently  know) 
in  which  we  have  less  than  16  parts  of  oxygen  in  each  molecule. 
If,  therefore,  we  place  the  weight  of  one  atom  of  hydrogen  at 
unity  (one-half  the  molecular  weight),  we  have  every  reason  to  sup- 
pose that  one  atom  of  oxygen  weighs  16  times  as  much  as  that  unit. 
In  one  molecule  of  water  we  therefore  have  two  ato?ns  of  hydrogen 
and  one  of  oxygen. 

The  relative  weight  of  a  molecule  of  hydrogen  chloride  is  36.5. 
This  molecule  contains  one  part  of  hydrogen  and  35.5  of  chlorine. 
The  maximum  atomic  weight  of  chlorine  is,  therefore,  35.5 ;  and 
as  we  have  never  encountered  less  than  this  quantity  of  chlorine 
united  with  one  part  of  hydrogen  or  its  equivalent  in  any  gasifi- 
able  chlorine  compound,  we  must  conclude  that  35.5  is  the  mini- 
mum. One  atom  of  chlorine,  therefore,  weighs  35.5  times  as 
much  as  an  atom  of  hydrogen,  and  in  one  molecule  of  hydro- 
gen chloride  we  have  one  atom  of  hydrogen  and  one  atom  of 
chlorine. 

The  relative  weight  of  a  molecule  of  ammonia  is  17  ;  this  mole- 
cule contains  three  parts  of  hydrogen  to  14  of  nitrogen.  The 
maximum  atomic  weight  of  nitrogen  is,  therefore,  14,  and  for 
reasons  similar  to  those  given  with  oxygen  and  chlorine,  its  mini- 
mum is  also  14.  One  molecule  of  ammonia,  then,  contains  three 
atoms  of  hydrogen  and  one  atom  of  nitrogen. 

The  above  table  now  shows  us  that  the  relative  mo- 
lecular weights  of  the  elements,  chlorine,  oxygen,  and 
nitrogen,  represent  numbers  which  are  twice  as  large  as 
the  relative  atomic  weights  of  those  elements  as  deter- 


134  ELEMENTS   OF  CHEMISTRY. 

mined  from  their  hydrogen  compounds.  Therefore,  the 
molecules  of  these  elementary  gases  contain  at  least  two 
atoms.  We  can  now  construct  the  following  table  :  *  — 

The  weight  of  an  atom  of  hydrogen  is  placed  =  1. 


ELEMENTS. 

ATOMIC  WEIGHT. 

MOLECULAR  WEIGHT. 

Hydrogen      .     .     . 
Chlorine  .... 

1. 
35.5 

2. 
71. 

Oxygen     .... 
Nitrogen  .... 

16. 
14. 

32. 

28. 

Chemical  notation  can  be  very  much  simplified  if  we 
represent  the  atoms  of  each  of  the  elements,  with  the 
atomic  weights  of  which  we  are  acquainted,  by  means 
of  certain  symbols.  The  system  universally  adopted  is 
one  which  uses  the  first  letter  of  the  English,  Latin,  or 
Latinized  name  of  the  element  in  question ;  i.e.,  H  rep- 
resents one  atom  of  hydrogen,  O  one  atom  of  oxygen, 
etc.t  The  structure  of  the  molecules  of  the  elements 
is  then  expressed  by  writing  after  the  symbol  a  sub- 
script number,  representing  the  number  of  atoms  in  the 
molecule ;  e.g.,  H2  represents  one  molecule  of  hydrogen, 
O2  one  molecule  of  oxygen,  N2  one  molecule  of  nitro- 
gen. The  molecules  of  compounds  are  represented  by 
writing  the  symbols  of  the  elements  entering  into  their 
formation  side  by  side,  with  the  subscript  numbers  rep- 

*  The  relative  weights  of  the  atoms  of  the  different  elements,  measured 
hy  some  standard  atomic  weight  (in  this  case  by  hydrogen  =  1),  are  for 
purposes  of  simplicity  termed  the  atomic  weights.  This  expression  will 
he  used  in  the  future.  For  the  same  reason  the  relative  molecular  weights 
are  termed  molecular  weights. 

t  In  some  cases  the  first  letter  of  the  Latin  name  is  used ;  e.g.,  K  for 
Kalium  (Latin  for  Potassium),  Na  for  Natrium  (Sodium).  Where  sev- 
eral elements  have  the  same  initial  a  second  letter  may  he  added;  C  = 
Carbon;  Cl  =  Chlorine;  Cu  =  Copper;  Ca  —  Calcium. 


DETERMINATION  OF  ATOMIC    WE IG PITS.        185 

resenting  the  number  of  atoms  entering  into  their  for- 
mation after  the  respective  symbols;  i.e.,  H2O  represents 
one  molecule  of  water  containing  two  atoms  of  hydro- 
gen and  one  of  oxygen ;  H  Cl,  one  molecule  of  hydrogen 
chloride  containing  one  atom  of  hydrogen  and  one  of 
chlorine.  NH3,  one  molecule  of  ammonia  containing 
one  atom  of  nitrogen  and  three  of  hydrogen.  As  these 
symbols  represent  the  uniting  atoms,  they  must  of  ne- 
cessity also  stand  for  the  atomic  weights.  For  exam- 
ple, the  combination  H2  O  means,  not  only  that  two 
atoms  of  hydrogen  with  one  atom  of  oxygen  form  one 
molecule  of  water,  but  it  also  represents  the  fact  that 
two  parts  of  hydrogen  are  united  with  16  of  oxygen  to 
produce  18  of  water. 

Determination  of  the  Number  of  Atoms  united  in  Mole- 
cules by  considering  the  Combining  Volumes  of  Gases.  We 
arrive  at  the  same  conclusions  regarding  the  number  of 
atoms  uniting  to  form  the  molecules  of  the  gaseous 
compounds  which  we  have  studied,  if  we  take  into  con- 
sideration the  combining  volumes  of  the  elementary 
gases  without  regard  to  their  specific  gravities.  This 
will  be  clear  from  the  following  reasoning :  — 

Composition  of  Hydrogen  Chloride.  We  learned  (page  41)  that 
hydrogen  chloride  is  produced  by  the  union  of  equal  volumes  of 
hydrogen  and  of  chlorine.  From  the  principles  of  the  kinetic 
gas  theory,  this  must  mean  that  equal  numbers  of  molecules  of 
hydrogen  and  chlorine  react  to  form  hydrogen  chloride;  i.e.,  one 
molecule  of  hydrogen  with  one  molecule  of  chlorine.  We  have 
also  learned  that  the  volume  of  hydrogen  chlorine  which  results  is 
twice  as  great  as  the  initial  volume  of  hydrogen,  so  that  there 
must  be  formed  twice  as  many  molecules  of  hydrogen  chloride  as 
there  were  either  of  hydrogen  or  of  chlorine.  One  molecule  of 
hydrogen,  which  contains  two  atoms,  with  one  molecule  of  chlo- 


136 


ELEMENTS    OF  CHEMISTRY. 


rine,  which  contains  two  atoms,  therefore,  produces  two  molecules 
of  hydrogen  chloride,  which  contain  each  one  atom  of  hydrogen 
and  one  of  chlorine.  This  result  can  be  expressed  by  chemical 
notation  as  follows  :  — 


H2         +         C12 

1  mol.  of  hydrogen  +  1  mol.  of  chlorine 


HC1  +  HC1. 

2  molecules  of  hydrogen  chloride. 


Now  let  us  suppose  that  the  volume  of  hydrogen  which  we  se- 
lected weighs  two  grams.  From  the  preceding  tables,  we  know 
that  an  equal  volume  of  chlorine  must  weigh  71  grams.  The  two 
grams  of  hydrogen  uniting  with  71  grams  of  chlorine  produce  73 
grams  of  hydrogen  chloride,  which  73  grams  occupy  twice  the 
volume  taken  by  two  grams  of  hydrogen,  and,  consequently,  a 
volume  of  hydrogen  chloride  equal  to  that  of  two  grams  of  hydro- 
gen would  weigh  36.5  grams.  The  specific  gravity  of  hydrogen 
chloride  (hydrogen  =  2)  is  therefore  36.5.  Hence  the  molecular 
weight  of  hydrogen  chloride  is  also  36.5,  a  conclusion  which  we 
reached  by  direct  comparison  in  the  first  portion  of  this  chapter. 


Composition  of  One  Molecule  of  Water.  We  learned  that  water 
is  produced  by  the  union  of  two  volumes  of  hydrogen  and  one  of 
oxygen,  hence,  in  its  formation,  two  molecules  of  hydrogen  react 
with  one  molecule  of  oxygen.  The  volume  of  water  vapor  which 
results  is  equal  to  that  of  the  hydrogen  with  which  we  started ;  i.e., 
it  is  two  volumes,  and  hence  represents  two  molecules.  One 
molecule  of  oxygen  with  two  molecules  of  hydrogen,  therefore, 
produces  two  molecules  of  water.  This  result  can  be  expressed 
as  follows  :  — 

H2         +          H2          +02  =H,0  +  H20. 

1  mol.  of  hydrogen  + 1  mol.  of  hydrogen  +  1  mol.  of  oxygen  =  2  mols.  of  water. 


2  grams  hydrogen  +  2  grams  hydrogen  +  32  grams  oxygen  =  18  grams  water  + 18  grams  water. 


DETERMINATION  OF  ATOMIC    WEIGHTS.        137 

If,  now,  one  of  these  volumes  of  hydrogen  weighs  2  grams, 
then  the  same  volume  of  oxygen,  as  we  have  seen,  weighs  32 
grams,  and  4  grams  of  hydrogen  with  32  grains  of  oxygen  pro- 
duce 36  grams  of  water  vapor.  This  quantity,  however,  occupies 
twice  the  volume  taken  by  2  grams  of  hydrogen.  Hence  the 
weight  of  a  volume  of  water  vapor  equal  to  that  of  2  grains  of 
hydrogen  is  18  grams.  The  specific  gravity  of  wrater  vapor  (hy- 
drogen =  2)  is  consequently  18,  and  the  relative  weight  of  a 
molecule  of  water  is  also  18. 


Composition  of  One  Molecule  of  Ammonia.  Three  volumes  of 
hydrogen  and  one  of  nitrogen  unite  to  form  two  volumes  of 
ammonia.  (See  page  94.)  Three  molecules  of  hydrogen,  there- 
fore, react  with  one  molecule  of  nitrogen  to  form  two  molecules 
of  the  compound.  As  one  molecule  of  nitrogen  is  capable  of 
forming  two  molecules  of  ammonia,  it  must  follow  that  each 
nitrogen  molecule  is  divisible  into  at  least  two  parts,  so  that  each 
must  contain  at  least  two  atoms  of  the  element.  As  each  hydro- 
gen molecule  also  contains  two  atoms,  the  formation  of  ammonia 
can  be  represented  as  follows  :  — 


H2  +  H2  +  H2  +  N2  =  NH3 

3  mols.  hydrogen  +1  mol.  nitrogen     =  2  mols.  of  ammonia. 


j  o 

a! 


4  o 
p  o 

~  % 


If  one  volume  of  hydrogen  weighs  two  grams,  an  equal  volume 
of  nitrogen  \veighs  28  grams.  Therefore  6  grams  of  hydrogen 
with  28  grams  of  nitrogen  produce  34  grams  of  ammonia.  This 
quantity  of  ammonia  occupies  twice  the  volume  of  two  grams  of 
hydrogen,  hence  the  weight  of  a  volume  of  ammonia  equal  to  that 
of  two  grams  of  hydrogen  is  17.  The  specific  gravity  of  ammo- 
nia (hydrogen  =  2)  is  therefore  17,  and  its  molecular  weight  is 
also  17. 

Summary. 

1.  Each  molecule  of  hydrogen  consists  of  at  least 
two  atoms. 


138  ELEMENTS   OF  CHEMISTRY. 

2.  The  weight  of  a  molecule  of  hydrogen  is  twice 
the  weight  of  one  atom.     The  weight  of  a  molecule  of 
hydrogen  is  the  standard  for  measuring  other  molecular 
weights. 

3.  If  hydrogen  as  2  is  made  the  standard  for  measur- 
ing the  specific  gravity  of  gases,  then  the  specific  gravity 
of  any  gas  is  the  same  as  its  molecular  weight. 

4.  The  determination  of  the  specific  gravities,  and 
hence  of  the  molecular  weights  of  gaseous  compounds, 
gives  us  a  means  of  ascertaining  the  maximum  numbers 
to  be  assigned  to  the  relative  weights  of  the  atoms  of 
the  elements.    The  minimum  numbers  for  these  relative 
atomic  weights  are  fixed  by  reasoning  that,  because  we 
find  no  gaseous  compounds  which  have  less  than  these 
minimum  quantities  of  the  elements  in  one  molecule, 
therefore  no  smaller  quantities  need  be  considered. 

5.  The  molecules  of  the  elements,  chlorine,  oxygen, 
and  nitrogen,  consist  of  at  least  two  atoms. 

.6.  One  atom  of  each  of  the  different  elements  can  be 
represented  by  an  appropriate  symbol.  The  molecules 
formed  by  the  union  of  these  atoms  can  be  represented 
by  joining  together  the  symbols,  with  subscript  numbers 
after  each.  These  numbers  indicate  the  number  of 
atoms  of  each  element  which  enters  into  a  molecule 
of  the  compound. 

7.  The  number  of  atoms  united  in  the  molecule  of 
gaseous  compounds  can  be  ascertained  by  a  proper  con- 
sideration of  the  combining  volumes  of  the  gaseous 
elements. 


THE  EXPRESSION  OF  CHEMICAL    CHANGES.     139 


CHAPTER   XVIII. 

THE   EXPRESSION   OF   CHEMICAL   CHANGES   BY 
FORMULAE  AND  EQUATIONS. 

THE  various  considerations  advanced  in  the  preceding 
chapter  have  shown  us  that  the  proper  interpretation 
of  the  relationships  between  the  combining  volumes 
of  gases,  and  the  volumes  of  the  compounds  produced 
by  such  combinations,  determines  the  molecular  weights 
of  those  compounds.  Knowing  the  molecular  weights, 
and  also  the  relative  parts  by  weight  in  which  the  ele- 
ments unite,  we  can,  therefore,  form  a  conclusion  as  to 
the  number  of  atoms  in  each  molecule,  and  as  to  the 
relative  atomic  weights.  These  results,  so  far  as  we 
have  gone,  can  be  summed  up  in  the  following  table :  — 


S3 

•<     03 

J    H 

FORMULAE. 

ij  53 

O   o 

COMPOSITION 

ATOMIC  WEIGHTS, 

3  3 

BY  WEIGHT. 

H  =  1. 

a* 

Hydrogen  chloride,  HC1 

3G.5 

1  part  H,  35.5  Cl 

Chlorine,  35.5 

Water,  H2O 

18. 

2  parts  H,  16  O 

Oxygen,     16. 

Ammonia,  H3  N 

17. 

3  parts  H,  14  N 

Nitrogen,  14. 

Composition  of  the  Molecules  of  Sulphur  Dioxide  and  Sul- 
phur Trioxide.  In  our  previous  work  we  have  repeatedly 
had  occasion  to  mention  two  other  gasifiable  compounds 
(sulphur  dioxide  and  sulphur  trioxide).  With  our 


140  ELEMENTS   OF  CHEMISTRY. 

present  knowledge  we  are  in  a  position  to  determine 
the  number  of  atoms  of  sulphur  and  of  oxygen  which 
are  combined  in  these  two  substances. 

Sulphur  Dioxide.  Sulphur  dioxide  is  produced  by  burning  sul- 
phur in  oxygen ;  and  if  care  is  taken  to  determine  the  relationship 
between  the  volume  of  oxygen  used  in  the  combustion,  and  the 
volume  of  sulphur  dioxide  produced,  we  shall  arrive  at  the  follow- 
ing results :  — 

When  sulphur  and  oxygen  unite  to  produce  sulphur  dioxide, 
the  volume  of  sulphur  dioxide  formed  is  the  same  as  the  volume 
of  oxygen  with  wrhich  we  started.  (See  page  54.) 

As  the  volume  of  oxygen  and  sulphur  dioxide  are  equal,  it  fol- 
lows the  sulphur  dioxide  must  contain  exactly  as  many  molecules 
as  did  the  oxygen.  Let  us  suppose  that  a  volume  of  oxygen  con- 
tains one  hundred  molecules.  Then  the  sulphur  dioxide  which 
would  be  produced  by  burning  sulphur  in  this  same  volume  would 
also  contain  one  hundred  molecules.  It  follows  from  this  that 
one  molecule  of  sulphur  dioxide  contains  one  molecule  of  oxygen. 
But  as  we  have  seen  that  one  molecule  of  oxygen  contains  two 
atoms,  it  follows  that  one  molecule  of  sulphur  dioxide  has  two 
atoms  of  oxygen.  We  have  decided  that  the  atomic  weight  of 
oxygen  is  16,  provided  that  of  hydrogen  be  considered  as  one. 
Therefore  two  atoms  of  oxygen,  measured  in  the  hydrogen  stand- 
ard, would  weigh  32.  Since  sulphur  dioxide  has  equal  parts  of 
sulphur  and  of  oxygen,  we  can  say,  in  terms  of  the  atomic  theory, 
that  32  parts  of  sulphur  are  joined  to  32  parts  of  oxygen  in  sulphur 
dioxide.  Xow,  it  can  be  decided  that  32  represents  the  weight  of 
one  atom  of  sulphur,  hydrogen  representing  unity ;  for  in  no  com- 
pound of  sulphur  which  is  a  gas,  and  the  molecular  weight  of 
which  we  consequently  know,  do  we  find  less  than  32  parts  by 
weight  of  sulphur  in  one  molecule.  The  specific  gravity  of  sul- 
phur dioxide  (hydrogen  =  2)  is  64.  In  64  parts  of  sulphur  diox- 
ide there  are  32  parts  of  sulphur  and  32  of  oxygen.  It  follows 
from  this  that  the  atomic  weight  of  sulphur  cannot  be  more  than 
32,  for  otherwise  we  should  have  to  accept  the  existence  of  a  frac- 
tion of  an  atom  of  sulphur  in  one  molecule  of  sulphur  dioxide. 
Therefore,  the  composition  of  sulphur  dioxide  is  such  that  one 
atom  of  sulphur  is  joined  to  two  atoms  of  oxygen  in  each  mole- 


THE  EXPRESSION  OF  CHEMICAL    CHANGES.    141 

cule.     This  result  can  be  expressed  by  the  following  formula  (in 
which  S  represents  one  atom  of  sulphur)  SO2- 

Sulphur  Trioxide.  When  sulphur  dioxide  is  changed  into  sul- 
phur trioxide,  it  adds  oxygen  in  such  quantity  that  the  resulting 
compound  contains  for  every  one  part  of  sulphur,  1.5  parts  by 
weight  of  oxygen.  Therefore  (the  32  parts  by  weight  of  sulphur 
in  64  of  sulphur  dioxide  remaining  unchanged),  sulphur  trioxide 
contains  32  parts  of  sulphur  to  48  of  oxygen  (1  : 1.5).  Now,  32 
represents  the  relative  weight  of  a  sulphur  atom,  measured  in  the 
hydrogen  standard,  and  48  =  (3  x  16)  represents  the  relative  weight 
of  three  oxygen  atoms.  Hence  a  molecule  of  sulphur  trioxide 
contains,  for  every  atom  of  sulphur,  three  atoms  of  oxygen.  The 
specific  gravity  of  sulphur  trioxide  in  the  form  of  a  gas  is  80 
(hydrogen  =  2),  so  that  its  molecular  weight  is  also  80  (H2=  2). 
In  80  parts  of  sulphur  trioxide  there  are  32  parts  of  sulphur  and 
48  parts  of  oxygen.  A  molecule  of  sulphur  trioxide  is  therefore 
represented  by  the  formula  SO3. 

Formation  of  Sulphuric  Acid  from  Sulphur  Trioxide  and  Water. 
Sulphur  trioxide  unites  with  water  to  produce  sulphuric  acid. 
(See  page  56.)  This  change  is  of  such  a  nature  that  80  parts 
of  sulphur  trioxide  take  up  18  parts  of  water  to  produce  98  parts 
of  pure  sulphuric  acid.  Eighty  represents  the  relative  weight  of 
one  molecule  of  sulphur  trioxide,  and  18  that  of  one  molecule  of 
water.  This  change  can  therefore-  be  represented  as  follows  :  — 

H2O  +  SO3  —  H2  S()4  * 

Sulphuric  acid,  therefore,  contains,  for  every  two  atoms  of  hydro- 
gen, one  of  sulphur,  and  four  of  oxygen. 

Relative  Atomic  Weights  of  Sodium  and  Potassium.  In 
order  to  complete  our  understanding  of  the  chemical 
changes  discussed  in  the  preceding  chapters,  it  is  'neces- 
sary to  determine  the  relative  weights  of  the  atoms  of 
potassium  and  sodium.  This. is  not  easily  accomplished 

*  In  the  member  at  the  right  of  the  sign  of  equality  we  have  simply 
added  the  two  terms  at  the  left.  The  masses  of  matter  on  both  sides  are 
therefore  equal. 


142  ELEMENTS   OF  CHEMISTRY. 

for  gasifiable  compounds  of  the  elements  in  question  are 
not  to  be  obtained  by  simple  means.  However,  sufficient 
data  are  at  hand  to  warrant  our  forming  a  conclusion. 

An  element  known  as  iodine  exists  which  is,  in  all  of  its  chem- 
ical aspects,  similar  to  chlorine.  Iodine  forms  a  hydrogen  com- 
pound, hydrogen  iodide,  \vhich  is  a  gas  like  hydrogen  chloride. 
Reasoning  similar  to  that  advanced  under  hydrogen  chloride  has 
led  us  to  the  conclusion  that  one  molecule  of  hydrogen  iodide 
contains  one  atom  of  hydrogen  and  one  atom  of  iodine.  The  mo- 
lecular weight  of  hydrogen  iodide  (H2=  2)  is  127.5.  This  quan- 
tity of  hydrogen  iodide  contains  one  part  of  hydrogen  and  12G.5 
parts  of  iodine.  Therefore,  the  relative  weight  of  one  atom  of 
iodine  is  126.5,  hydrogen  being  one.  ISTow,  potassium  reacts  with 
hydrogen  iodide  just  as  it  does  with  hydrogen  chloride,  replacing 
the  hydrogen  and  producing  potassium  iodide.  Potassium  iodide, 
when  changed  to  a  gas  by  great  heat,  has  a  specific  gravity  (hy- 
drogen =  2)  of  165.5,  hence  its  molecular  weight  (H2  =  2)  is  also 
165.5.  In  165.5  parts  of  potassium  iodide  there  are  126.5  of 
iodine  (the  proportional  part  representing  one  atom  of  iodine)  and 
39  parts  of  potassium.  In  the  absence  of  any  evidence  to  the 
contrary,  39  may,  therefore,  be  regarded  as  the  relative  weight  of 
one  atom  of  potassium. 

Action  of  Potassium  and  Sodium  on  Water  in  Terms  of  the 
Atomic  Theory.  When  potassium  acts  upon  water,  one-half  the 
hydrogen  in  the  water  attacked  is  replaced  by  potassium.  An 
analysis  of  the  product  (potassium  hydroxide)  shows  us  that  39 
parts  of  the  metal  take  the  place  of  one  part  of  hydrogen.  If  39 
and  one  represent  the  atomic  weights  of  potassium  and  of  hydro- 
gen respectively,  then  one  atom  of  potassium  replaces  one  atom  of 
hydrogen  in  eacn  molecule  of  water.  This  change  can  be  repre- 
sented as  follows :  — 

K  +      HOH  KOH  4-  H. 

1  atom  of  potassium  *  +  1  mol.  of  water  =  1  mol.  of  potassium  hydroxide  +  1  atom  of  hydrogen. 

Potassium  hydroxide,  therefore,  can  be  considered  as  water,  in 
each  molecule  of  which  one  atom  of  hydrogen  has  been  replaced 

*  K  represents  one  atom  of  potassium,  atomic  weight  39.  This  sym- 
bol is  taken  from  the  Latin  Kalium. 


THE  EXPEESSION  OF  CHEMICAL    CHANGES.    143 

by  one  atom  of  potassium.  From  the  great  similarity  between 
potassium  hydroxide  and  sodium  hydroxide,  it  may  be  presumed 
that  they  are  alike  in  their  constitution.  The  latter  then  may  be 
regarded  as  water,  in  each  molecule  of  which  one  atom  of  sodium 
has  taken  the  place  of  one  atom  of  hydrogen.  As  23  parts  of 
sodium  replace  one  part  of  hydrogen,  it  may  also  be  presumed  that 
the.  atomic  weight  of  sodium  is  23  if  that  of  hydrogen  is  one. 
The  action  of  sodium  on  water  can,  therefore,  be  represented  as 

follows :  *  — 

Xa  4-  HOH  =  Na  OH  +  H. 

Neutralization  of  Hydrochloric  Acid  in  Terms  of  the  Atomic 
Theory.  When  sodium  hydroxide  acts  on  hydrochloric  acid  the 
latter  is  neutralized  (see  page  48),  and  the  resulting  salt  (sodium 
chloride)  contains  23  parts  of  sodium  for  every  35.5  parts  of  chlo- 
rine. These  parts  also  represent  the  relative  atomic  weights  of 
sodium  and  chlorine,  so  that  sodium  chloride  is  produced  by  the 
union  of  equal  numbers  of  sodium  and  chlorine  atoms,  and  its 
formula  is  represented  by  Na  Cl.  The  neutralization  of  sodium 
hydroxide  by  hydrogen  chloride  can  now  be  written  in  terms  of 
the  atomic  theory  as  follows  :  — 

Na  OH  +  H  Cl  =  Na  Cl  +  HOH. 

Adding  the  atomic  weights  of  the  members  to  the  left  of  the  sign 
of  equality,  and  doing  the  same  with  those  on  the  right,  we  have  — 

Sodium,  atomic  weight,  23  Sodium,  atomic  weight,  23 

Oxygen,  atomic  weight,  16  Chlorine,  atomic  weight,  35.5 

Hydrogen,  atomic  weight,  1  Sodium  chloride,  total,    58.5 

Sodium  hydroxide,  total,  40 

Chlorine,  atomic  weight,  35.5  Oxygen,  atomic  weight,  16 
Hydrogen,  atomic  weight,  1  Hydrogen,  two  atoms,  2 
Hydrochloric  acid,  total,  36.5  Water,  total,  18 

40  +  36.5  =  58.5  +  18. 

According  to  this  equation,  therefore,  40  parts  of  sodium  hydrox- 
ide will  exactly  neutralize  36.5  parts  of  hydrochloric  acid,  produ- 
cing 58.5  parts  of  sodium  chloride  and  18  parts  of  water.  This 

*  The  symbol  Na  represents  one  atom  of  sodium,  atomic  weight  23. 
This  symbol  is  taken  from  the  Latin  Natrium. 


144  ELEMENTS   OF  CHEMISTRY. 

theoretical  result  is  exactly  in  accordance  with  what  we  actually 
found  in  the  experiments  on  neutralization  (see  page  62).  No 
other  conclusion  is  admissible,  since  the  atomic  theory  to  have 
any  stability  must  of  necessity  coincide  with  known  facts. 

Neutralization  of  Sulphuric  Acid  by  Sodium  and  Potassium  Hy- 
droxide in  Terms  of  the  Atomic  Theory.  In  neutralizing  sulphuric 
acid  with  potassium  hydroxide  or  sodium  hydroxide,  we  learned 
that  two  salts  of  each  metal  could  be  produced.  These  salts  were 
designated  as  being  primary  and  secondary.  In  the  primary  salt, 
one-half  the  hydrogen  of  the  combining  sulphuric  acid  is  replaced 
by  the  metal  (sodium  or  potassium).  In  the  secondary  salt,  all  the 
hydrogen  is  so  replaced.  In  terms  of  the  atomic  theory,  we  can 
express  these  facts  as  follows  :  — 

1  (  Na  OH  4-      Ho  SO4  =  ISTa  HSO4  +  H2  O. 

I  Na  OH  4-  Na  HSO4  =  Na2  SO4    +  H2  O. 


2  fKOH  +  H2S04   =KHS04  +  H20. 

I  KOH  4-  KHSO4  =  K2  SO4  +  H2  O. 

Adding  the  members  to  the  right  and  those  to  the  left  of  the  sign 
of  equality  as  we  did  before,  we  have  — 

Sodium,  atomic  weight,  23  Sodium,  atomic  weight,  23 

Oxygen,  atomic  weight,  16  Sulphur,  atomic  weight,  32 

Hydrogen,  atomic  weight,  1  4  atoms  of  oxygen,  64 

Sodium  hydroxide,  total,  40  Hydrogen,  atomic  weight,  1 

Primary  sod.  sulphate,  total,  120 

Sulphur,  atomic  weight,  32 

4  atoms  of  oxygen,  64  Oxygen,  atomic  weight,  1  6 

2  atoms  of  hydrogen,  2  2  atoms  of  hydrogen,  2 

Sulphuric  acid,  total,  98  Water,  total,  18 

and  —  40  4-  98  =  120  4-  18. 

In  forming  the  secondary  sulphate  of  sodium,  we  would,  therefore, 

have  — 

Sodium  hydroxide,  80  parts  by  weight, 
Sulphuric  acid,  98  parts  by  weight, 
Secondary  sodium  sulphate,  142  parts  by  weight, 
Two  molecules  of  water,  36  parts  by  weight, 

and  — 

80  4-  98  =  142  +  36. 


THE  EXPRESSION  OF  CHEMICAL   CHANGES.    145 

So  that  40  and  80  parts  of  sodium  hydroxide  are  capable  of 
reacting  with  98  parts  of  sulphuric  acid  to  produce  120  and  142 
parts  of  the  primary  and  the  secondary  sulphate  of  sodium  re- 
spectively. These  results  are  in  accordance  with  those  which  we 
found  experimentally  on  page  63.  With  potassium  hydroxide 
and  sulphuric  acid  we  have  — 

Potassium,  atomic  weight,  39  Potassium,  atomic  weight,    39 

Oxygen,  atomic  weight,       16  Sulphur,  atomic  weight,         32 

Hydrogen,  atomic  weight,     1  4  atoms  of  oxygen,  64 

Potassium  hydroxide,  total,  56  Hydrogen,  atomic  weight,  1 

Potass,  pr.  sulphate,  total,     136 
Sulphur,  atomic  weight,      32 

4  atoms  oxygen,  64  Oxygen,  atomic  weight,         16 

2  atoms  of  hydrogen.  2  2  atoms  of  hydrogen,  2 

Sulphuric  acid,  total,  "98  Water,  total,  18 

56  +  98  =  136  -f  18. 

In  forming  the  secondary  sulphate  of  potassium  we  should,  there- 
fore, have  — 

Potassium  hydroxide,  112  parts, 

Sulphuric  acid,  98  parts, 

Secondary  potassium  sulphate,  174  parts, 

Two  molecules  of  water,  36  parts, 

112  +  98  =  174  +  36. 

So  that  56  and  112  parts  of  potassium  hydroxide  are  capable  of 
reacting  with  98  parts  of  sulphuric  acid  to  produce  136  and  174 
parts  of  the  primary  and  secondary  sulphate  of  potassium  respec- 
tively. These  results  are  in  accordance  with  those  which  we 
found  experimentally  on  page  63. 

Formation  of  Ammonium  Chloride  in  Terms  of  the  Atomic 
Theory.  The  only  remaining  compound  which  was  discussed  at 
length  in  the  preceding  work  is  ammonium  chloride.  This  sub- 
stance is  produced  by  the  union  of  equal  volumes  of  ammonia  and 
hydrogen  chloride,  therefore  it  is  formed  from  equal  numbers  of 
molecules  of  ammonia  and  hydrogen  chloride.  In  other  words, 
one  molecule  of  ammonia  with  one  molecule  of  hydrogen  chloride 
forms  one  molecule  of  ammonium  chloride.  Under  proper  condi- 


146 


ELEMENTS  OF  CHEMISTRY. 


tions  ammonium  chloride  can  be  vaporized  without  change.  Its 
specific  gravity  (hydrogen  =  2)  is  then  53.5,  so  that  its  molecular 
weight  is  also  53.5.  In  this  5.35  parts  of  ammonium  chloride 
there  are  14  of  nitrogen,  4  of  hydrogen,  and  35.5  of  chlorine. 
The  composition  of  one  molecule  of  ammonium  chloride  can, 
therefore,  be  represented  by  the  formula  NH4  Cl,  and  its  forma- 
tion from  ammonia  and  hydrogen  chloride  as  follows  :  — 

NH3  +  H  Cl  =  NH4  Cl. 

The  group  of  elements  NH4,  composed  of  one  atom  of  nitrogen 
and  four  of  hydrogen,  is  the  one  which  under  the  name  of  am- 
monium can  take  the  place  of  one  atom  of  potassium  or  sodium 
in  chemical  compounds.  (See  page  99.) 

Table  of  Atomic  Weights  and  Formulae  of  Compounds 
already  studied.  The  atomic  weights  of  the  elements 
which  we  have  encountered,  the  formulae  of  the  com- 
pounds, and  the  reactions  leading  to  their  formation, 
are  summed  up  in  the  following  table :  — 

HYDROGEN  ATOMIC  WEIGHT  =  1. 


ELEMENTS. 

SYMBOLS. 

ATOMIC 
WEIGHTS. 

COMPOUNDS. 

FORMULA. 

COMPOSITION  BY 
WEIGHT. 

Chlorine 

Cl 

35.5 

Hydrogen  chloride 

HC1 

1    of   hydrogen,  35.5  of 

chlorine. 

Oxygen 

0 

16 

Water 

H20 

2    of    hydrogen,    16   of 

oxygen. 

Nitrogen 

N 

14 

Ammonia 

H3N 

3  of  hydrogen,  14  of  ni- 

trogen. 

Sodium 

Na 

23 

Sodium  hydroxide 

NaOH 

23  of  sodium,  16  of  oxy- 

gen, 1  of  hydrogen. 

Potassium 

K 

39 

Potassium 

KOH 

39  of    potassium,   16  of 

oxygen,  1  of  hydro- 

gen. 

1  Sulphur  dioxide 

S02 

32  of  sulphur,  32  of  oxy- 

gen. 

Sulphur  trioxide 

S03 

32  of  sulphur,  48  of  oxy- 

Sulphur 

S 

32 

gen. 

Sulphuric  acid 

H2S04 

32  of  sulphur,  64  of  oxy- 

gen, 2  of  hydrogen. 

Ammonium  chloride 

NH4C1 

14  of    nitrogen,  35.5  of 

chlorine,  4  of  hydro- 

gen. 

THE  EXPRESSION  OF  CHEMICAL   CHANGES.     147 
REACTIONS. 

Na  +  HOH  =  Na  OH  +  H.  . 

Action  of  sodium  on  water,  1  atom  of  sodium  replacing  1  atom  hydrogen. 

K  +  HOH  =  KOH  +  H. 

Action  of  potassium  on  water,  1  atom  of  potassium  replacing  1  atom  hydrogen. 

Na  OH  +  H2  SO4  =  Na  HSO4  +  H2  O. 

Action  of  sodium  hydroxide  on  sulphuric  acid,  1  atom  of  sodium  replacing  1  atom  hydrogen. 

2  Na  OH  +  H2SO4  =  Na2  SO4  +  2  H2  O. 

Action  of  sodium  hydroxide  on  sulphuric  acid,  2  atoms  of  sodium  replacing  2  atoms  hydrogen. 

KOH  +  H2  SO4  —  KHSO4  +  H2  O. 

Action  of  potassium  hydroxide  on  sulphuric  acid,  1  atom  of  potassium  replacing  1  atom  hydrogen. 

2  KOH  +  H2  SO4  =  K2  SO4  +  2H2  O. 

Action  of  potassium  hydroxide  on  sulphuric  acid,  2  atoms  of  potassium  replacing  2  atoms  hydrogen. 

NH3  +  H  Cl  =  NH4  Cl. 

Action  of  ammonia  on  hydrogen  chloride,  forming  ammonium  chloride. 

Meaning  and  Uses  of  Chemical  Equations.  The  changes 
taking  place  during  chemical  reactions  can,  as  we  have 
seen,  be  expressed  in  the  form  of  equations.  To  the 
left  of  the  sign  of  equality  are  those  substances  which 
are  about  to  react  with  each  other,  to  the  right  are  the 
new  and  more  stable  bodies  which  result  from  those 
reactions.  The  same  elements  appear  in  both.  These 
equations  represent  what  takes  place  between  the  small- 
est particles  of  the  substances  taking  part  in  the  chemi- 
cal changes.  As  what  is  true  of  these  smallest  particles 
must  also  be  true  of  the  large  masses  which  are  com- 
posed of  them,  it  follows  that  these  equations  also 
represent  the  changes  which  take  place  in  visible  por- 
tions of  matter.  As  the  symbols  of  the  various  ele- 
ments represent  the  relative  atomic  weights  of  these 
elements,  the  equations  must  represent  both  the  relative 
weights  of  the  substances  which  are  reacting,  and  the 
relative  weights  of  the  masses  handled.  In  practice 
there  is  frequently  present  an  excess  of  one  or  the 
other  of  the  substances  undergoing  chemical  change ; 
but  as  such  an  excess  does  not  enter  into  the  chemical 
formation  of  the  compound  produced,  it  need  not  be 


ft 

148  ELEMENTS   OF  CHEMISTRY. 

considered  in  the  notation.  One  serious  defect  is  evi- 
dent in  equations  such  as  we  have  considered,  —  they 
do  not  take  cognizance  of  the  changes  of  energy  during 
chemical  reactions.  They  simply  concern  themselves 
with  the  reacting  masses.  Nevertheless,  they  give  us 
a  short  and  convenient  way  of  illustrating  one  of  the 
main  features  of  the  various  chemical  changes,  and 
involve  a  considerable  saving  in  time.  Two  things 
must  be  borne  in  mind ;  first,  chemical  notation  and 
chemical  equations  are  not  absolutely  essential  to  an 
understanding  of  chemical  change ;  secondly,  chemical 
equations  must  be  used  to  express  only  those  reactions 
which  have  actually  been  studied.  They  are  merely 
brief  and  convenient  ways  of  expressing  knowledge 
already  acquired  by  experiment.  The  careful  study  of 
all  the  phenomena  attending  a  chemical  change  must 
be  carried  out  before  the  results  of  such  a  study  can 
properly  be  brought  in  the  form  of  a  chemical  equation. 

Summary. 

The  changes  taking  place  during  chemical  reactions 
can  be  expressed  in  the  form  of  equations.  These  equa- 
tions do  not  consider  either  the  excess  of  one  or  the  other 
of  the  reacting  bodies,  or  the  changes  of  energy  which 
take  place  during  reactions.  They  do,  however,  express 
the  masses  of  the  bodies  undergoing  chemical  change, 
and  these  masses  must  be  in  accordance  with  facts  which 
have  been  experimentally  proven.  The  reactions  which 
have  been  encountered  in  this  book  are  given,  in  the 
form  of  equations,  on  pages  143,  144,  and  147. 

Having  discussed  the  atomic  theory,  the  next  step  in 
the  work  is  to  consider  the  chemistry  of  another  ele- 
ment, and  of  its  compounds. 


CAEBON.  149 


CHAPTER   XIX. 

CARBON. 

CAEBON  is  one  of  the  most  important  chemical  ele- 
ments. In  nature  it  occurs  uncombined  in  three  modi- 
fications, two  of  which  (diamond  and  graphite)  are  of 
crystalline  structure,  while  the  third  is  not  crystalline 
(coal,  charcoal,  lamp-black,  etc.). 

Various  Modifications  of  Carbon.  That  all  these  forms 
are  really  modifications  of  the  same  element  is  proved 
by  the  fact  that  they  all  yield  the  same  substance  (car- 
bon dioxide)  when  they  are  burned  in  oxygen.  By 
proper  means,  not-crystalline  carbon  can  be  regained 
from  carbon  dioxide,  no  matter  whether  it  has  been 
formed  by  the  combustion  of  diamond,  graphite,  or 
coal. 

Diamond.  The  diamond  is  an  extremely  hard  sub- 
stance, very  often  transparent,  with  a  great  power  of 
refracting  light,  and  brilliant  lustre  when  polished. 
Not-transparent  black  diamond  is  also  found.*  When 
heated  in  the  air  to  a  bright  white  heat,  diamond  burns, 
forming  carbon  dioxide,  and  leaving  only  a  slight  trace 
of  ash.  The  diamond  may  be  classed  among  the  rare 
minerals. 

*  Diamonds  were  originally  imported  into  Europe  from  the  East  Indies. 
From  this  portion  of  the,world  and  from  Borneo  came  the  only  specimens 
known  until  the  year  1727,  when  large  diamond  fields  were  discovered  in 
Brazil.  In  1867  the  diamond  fields  of  South  Africa  were  opened. 


150  ELEMENTS   OF  CHEMISTRY. 

Graphite.  Graphite  (also  called  plumbago  or  black 
lead)  is  the  second  crystalline  form  of  carbon.  Some- 
times graphite  is  found  in  a  pure  state,  as  in  some  parts 
of  Ceylon,  where  beds  of  from  twenty  to  thirty  feet  in 
thickness  occur.  Sometimes  it  is  very  impure,  being 
mixed  with  so  much  foreign  material  that  it  is  entirely 
unfit  for  use.  Graphite  may  be  artificially  prepared  by 
the  crystallization  of  carbon  from  melted  iron.  It  then 
can  be  separated  in  the  form  of  small,  delicate  scales 
when  the  iron  is  dissolved  away  by  acids.  Graphite  is 
used  in  the  manufacture  of  lead  pencils,  in  making  infu- 
sible crucibles,  and  as  a  lubricator.  It  is  adapted  to  the 
latter  purpose  because  it  is  soft  and  scaly.  It  is  grayish- 
black  in  color,  and  has  almost  a  metallic  lustre.  When 
burned  in  the  air  it  forms  carbon  dioxide,  and  leaves  an 
ash  which  varies  in  quantity  according  to  the  amount 
of  impurity  originally  present. 

Decomposition  of  Animal  and  Vegetable  Substances.  The 
compounds  formed  in  animal  and  vegetable  organisms, 
and  classed  under  the  general  head  of  organic  sub- 

^.        ^  . 

stances,  are  produced  by  the  union  of  very  few  ele- 
ments, namely,  carbon,  hydrogen,  oxygen,  nitrogen, 
sulphur,  and  phosphorus,  although  occasionally  other 
elements  are  found.  When  exposed  to  the  action  of 
moisture  and  of  the  air,  organic  substances  are  com- 
pletely decomposed,  changing  for  the  most  part  into 
gaseous  products  (carbon  dioxide,  ammonium  com- 
pounds, etc.).  Vegetable  fibres  when  protected  by  a 
layer  of  water  or  of  earth,  so  that  an  insufficient  supply 
of  oxygen  is  present,  decompose  very  slowly,  certain 
constituents,  especially  oxygen  and  hydrogen,  pass  off 
in  other  combinations,  and  the  vegetable  matter  be- 


CARBON.  151 

comes  changed,  first  into  peat,  and  then  into  bituminous 
(soft)  coal.  At  the  same  time  the  percentage  of  car- 
bon increases.  Peat,  brown  coal,  bituminous  coal,  and 
anthracite  coal  are  successive  steps  in  the  process  of 
vegetable  decomposition.  When  the  anthracite  stage  is 
reached,  the  changes  have  become  so  complete  that  a 
black,  shiny,  homogeneous  mass  remains,  and  the  origi- 
nal vegetable  structure  has  entirely  disappeared,  or  be- 
come so  indistinct  that  special  means  must  be  taken  for 
its  detection.  The  pressure  to 'which  the  dead  organic 
structures  are  subjected  has  a  material  influence  on  the 
rapidity  with  which  a  peat  formation  is  changed  to 
anthracite.  In  districts  of  Russia  where  there  has  not 
been  great  pressure,  a  brown  coal  (lignite),  scarcely  to 
be  distinguished  from  peat,  is  found  in  places  where  the 
age  of  the  deposit  would  lead  one  to  expect  anthracite.59* 

Formation  of  Coke.  Changes  similar  to  those  produced 
in  the  transformation  of  vegetable  matter  into  coal  can 
be  brought  about  by  heating  the  same  class  of  sub- 
stances in  retorts,  if  the  air  is  excluded.  By  means 
of  this  process,  certain  portions  pass  off  as  gases  and 
liquids,!  while*  a  not-crystalline  variety  of  carbon  is 

*  The  following  table  illustrates  the  increase  in  the  percentage  of  car- 
bon during  the  change  from  wood  to  anthracite  coal.    This  table  takes 
into  consideration  only  the  combustible  materials,  and  not  the  ash :  — 
Wood  contains  50  pei  cent  of  carbon,  6  per  cent  of  hydrogen,  and  44  per  cent 

of  oxygen  and  nitrogen. 
Peat  contains  60  per  cent  of  carbon,  5.7  per  cent  of  hydrogen,  and  34.3  per  cent 

of  oxygen  and  nitrogen. 
Bituminous  coal  contains  87  per  cent  of  carbon,  5.6  per  cent  of  hydrogen, 

and  7.4  per  cent  of  oxygen  and  nitrogen. 
Anthracite  contains  94  per  cent  of  carbon,  3.4  per  cent  of  hydrogen,  and  2.6 

per  cent  of  oxygen  and  nitrogen. 

t  Gaseous  products,  —  Illuminating  gas,  ammonia,  sulphuretted  hy- 
drogen, etc. 

Liquid  products, — Water,  benzene,  toluene,  carbolic  acid,  etc. 
Solid  products, — Naphthaline,  anthracene,  etc. 


152  ELEMENTS   OF  CHEMISTRY. 

left  behind  as  a  black  shiny  mass  termed  coke.  The 
commercial  production  of  coke  is  generally  brought 
about  by  heating  bituminous  coal. 

Charcoal.  Wood  charcoal  is  produced  by  the  imper- 
fect combustion  of  wood,  animal  charcoal,  by  a  similar 
treatment  of  animal  refuse.  All  forms  of  charcoal  have 
a  remarkably  pronounced  tendency  to  absorb  coloring 
matters  from  solutions.60 

Lamp-black.  The  purest  form  of  not^crystalline  car- 
bon is  lamp-black.  This  results  when  carbon  and  hy- 
drogen compounds  are  burned  in  an  imperfect  supply 
of  oxygen.  The  lamp-black  of  commerce  is  obtained  by 
burning  resinous  pine  wood,  tar,  or  some  kinds  of  bi- 
tuminous (soft)  coal.  The  substance  is  collected  on 
coarse  cloths  hung  over  the  burning  wood,  which  is 
placed  in  suitable  chambers.  Lamp-black  is  used  in 
the  manufacture  of  India  ink  and  printers'  ink. 


CARBON  DIOXIDE.  153 


CHAPTER   XX. 

CARBON  DIOXIDE 

CARBON  is  capable  of  forming  two  oxides  which  are 
distinguished  by  the  terms  carbon  monoxide  and  carbon 
dioxide.  Of  these  the  latter  is  the  easier  to  produce 
and  study.  A  consideration  of  the  former  will  be  post- 
poned to  a  subsequent  chapter. 

Formation  of  Carbon  Dioxide  and  the  Formula  for  one 
Molecule  of  Carbon  Dioxide.  When  carbon  is  burned  in 
the  air  or  in  oxygen,  it  unites  with  the  oxygen  to  pro- 
duce a  colorless  gas  which  is  an  oxide  of  carbon.  If 
the  combustion  takes  place  in  a  closed  space,  so  that 
the  volume  of  gas  present  at  the  beginning  of  the  opera- 
tion and  at  the  end  can  be  carefully  measured,  it  will 
be  seen  that  no  change  in  the  total  volume  has  oc- 
curred.61 All  of  the  oxygen  has  been  consumed,  and 
carbon  dioxide  has  taken  its  place.  A  similar  result, 
it  will  be  remembered,  was  encountered  in  studying 
the  formation  of  sulphur  dioxide  (see  page  54).  We 
are,  therefore,  justified  in  drawing  similar  conclusions 
as  to  the  structure  of  the  carbon  dioxide  molecules. 
We  can  assume  that  as  there  is  no  change  in  the  total 
volume  of  gas,  and  no  change  in  the  total  number  of 
molecules,  then  n  molecules  of  oxygen,  as  a  consequence, 
produce  n  molecules  of  carbon  dioxide,  and  (if  n  =  1) 
one  molecule  of  oxygen  enters  into  the  formation  of  one 


154  ELEMENTS   OF  CHEMISTRY. 

molecule  of  carbon  dioxide.  Since  one  molecule  of 
oxygen  contains  two  atoms,  it  must  follow  that  one 
molecule  of  carbon  dioxide  also  contains  two  atoms  of 
oxygen.  The  specific  gravity  of  carbon  dioxide  (hy- 
drogen =  2)  is  44.  Its  molecular  weight  (H2  =  2)  is 
also  44.  In  44  parts  of  carbon  dioxide  there  are  32  of 
oxygen  and  12  of  carbon.  Therefore,  12  represents  the 
maximum  atomic  weight  of  carbon,  provided  that  of 
hydrogen  is  one.  That  12  is  also  the  minimum  atomic 
weight  is  probable  from  the  fact  that  no  gasifiabLe  car- 
bon compound  contains  less  than  12  parts  of  carbon 
(measured  in  the  hydrogen  standard)  in  one  molecule. 
The  12  parts  of  carbon  in  the  molecule  of  carbon  diox- 
ide, therefore,  represent  one  atom  of  carbon,  and  the 
32  parts  of  oxygen  represent  two  atoms  of  oxygen,  and 
the  formula  for  carbon  dioxide  is  CO2.  This  formula, 
is,  therefore,  parallel  to  that  for  sulphur  dioxide :  — 

C02  S02 

Carbon  dioxide,  Sulphur  dioxide. 

Preparation  of  Carbon  Dioxide.  If  an  iron  tube  in  which  are 
placed  pieces  of  charcoal  be  heated  in  a  furnace,  and  pure  oxygen 
be  then  passed  over  the  hot  carbon,  the  carbon  dioxide  which  is 
formed  can  be  collected  in  bottles.  This  gas  has  a  higher  spe- 
cific gravity  than  the  atmosphere,  and  consequently  will  flow  down- 
ward, just  as  a  liquid  would.62 

Properties  of  Carbon  Dioxide.  Carbon  dioxide  is  a  colorless  gas 
with  a  specific  gravity  (air=  1)  of  1.529  or  (H2  =  2)  of  44.  The 
latter  number  is  a}so  its  molecular  weight.  Because  carbon  diox- 
ide has  such  a  high  specific  gravity,  it  can  be  poured  downward 
from  any  vessel  containing  it.  For  this  reason  it  collects  at  the 
bottoms  of  wells  or  mines  into  which  the  gas  is  escaping.  Carbon 
dioxide  does  not  burn  in  oxygen,  neither  does  it  give  up  any  por- 
tion of  its  oxygen  readily  enough  to  support  combustion.  Cold 
and  pressure  combined  can  condense  it  to  a  liquid  which  boils  at 


CARBON  DIOXIDE.  155 

—  78.2°.  Its  vapor  tension  (see  page  70)  at  0°  is  36  atmospheres, 
its  critical  temperature  *  is  39.9°,  and  its  vapor  pressure  at  this 
point  is  73  atmospheres.  When  carbon  dioxide  is  rapidly  evapo- 
rated in  a  vacuum,  its  temperature  sinks  to  —  97°,  and  it  then 
changes  to  a  snow-like  solid.  Any  considerable  increase  in  the 
quantity  of  carbon  dioxide  normally  present  in  the  air  (3  parts  in 
10,000,  see  page  84)  causes  a  marked  feeling  of  discomfort  to 
those  breathing  it,  and  a  proportion  of  approximately  10  per  cent 
will  cause  death.  The  reason  for  this  is  that  the  pressure  of  car- 
bon dioxide  in  the  inhaled  air  is  equal  to  that  of  the  carbon  diox- 
ide passing  off  from  the  lungs.  When  this  condition  is  reached, 
no  elimination  of  carbon  dioxide  can  take  place,  the  normal  pro- 
cesses of  life  are  interfered  with,  and  the  animal  dies.  Plants, 
when  placed  in  the  sunlight,  are,  on  the  other  hand,  capable  of  ab- 
sorbing carbon  dioxide,  changing  it  into  new  compounds  of  car- 
bon (which  form  a  portion  of  their  tissues),  and  eliminating  a 
portion  of  the  oxygen.  One  cubic  centimetre  of  water  can  dis- 
solve about  its  own  volume  of  carbon  dioxide  at  ordinary  tem- 
peratures. 

Formation  of  Carbonates  from  Carbon  Dioxide  and  Bases.  If 
carbon  dioxide  is  passed  into  a  solution  of  potassium  hydroxide, 
complete  absorption  takes  place.  If  this  operation  is  continued 
until  the  base  has  taken  up  all  the  gas  which  it  possibly  can,  and 
if  the  excess  of  water  used  for  solution  is  then  evaporated,  there 
remains  a  salt-like  body  which  differs  entirely  from  potassium 
hydroxide.  If  a  little  of  this  salt  is  placed  in  a  test-tube,  and 
some  solution  of  hydrochloric  acid  is  added,  a  violent  evolution  of 
gas  will  take  place.  This  gas  will  neither  burn  nor  support  com- 
bustion, and  in  all  its  properties  is  identical  with  carbon  dioxide. 
We  find,  therefore,  that  carbon  dioxide  can  unite  directly  with 
potassium  hydroxide  to  produce  a  new  body.  By  carefully  meas- 
uring the  quantity  of  carbon  dioxide  obtained  from  a  given  weight 
of  this  body  by  adding  hydrochloric  acid,  we  learn  that  exactly 
44  parts  of  carbon  dioxide  (representing  one  molecule)  have  united 
with  56  parts  of  potassium  hydroxide  (represented  by  the  formula 


*  I.e.,  the  temperature  above  which  no  pressure  can  convert  it  to  a 
liquid. 


156  ELEMENTS   OF  CHEMISTRY. 

KOH,  see  page  142).     The  reaction  which  takes  place  can  be  rep- 
resented as  follows :  — 

KOH          +       C02      =          KHC03 

potassium  hj'droxide  +  carbon  dioxide  =  The  product  of  addition. 
56  parts  -f         44  parts        =  100  parts. 

If,  now,  two  grams  of  this  salt  are  placed  in  a  test-tube  of  infu- 
sible glass,  and  then  gently  heated  to  below  red  heat,  a  gas  will  pass 
off  which  can  be  shown  to  have  the  properties  of  carbon  dioxide. 
At  the  same  time  water  is  formed,  as  can  be  seen  by  the  drops  of 
that  liquid  collected  on  the  sides  of  the  tube  in  which  the  salt  is 
heated.  After  no  more  carbon  dioxide  passes  off,  the  water  can  be 
removed  by  placing  the  tube  in  an  air-bath  heated  to  about  150°. 
After  cooling,  the  two  grams  of  the  salt  will  be  found  to  have  lost 
.62  grams  of  carbon  dioxide  and  water,  while  1.38  grams  of  a  sec- 
ond salt-like  body  will  remain.  This  body,  on  addition  of  hydro- 
chloric acid,  will  give  off  a  gas,  which  is  carbon  dioxide.  In  this 
respect  it  resembles  the  first  salt  which  was  formed.  The  change 
taking  place  on  heating  can  therefore  be  represented  as  follows : 

KHCO3  =  KjCOs  +       H2O       +  CO2 

2.00  parts     =  1.38  parts  of  the  second  salt  +  .18  parts  of  water  +  .44  parts  of  carbon  dioxide.ea 

The  Primary  and  Secondary  Carbonates  of  Potassium  are 
Salts  of  an  Acid,  H2C03.  The  two  salt-like  bodies  pro- 
duced, first  by  the  addition  of  carbon  dioxide  to  potas- 
sium hydroxide,  and  second  by  heating  the  substance  so 
formed,  can  be  considered  as  derived  from  an  acid  to 
which  we  assign  a  formula,  H2CO3.  This  acid  does 
not  in  reality  exist.  Whenever  any  attempts  have  been 
made  to  isolate  it  as  a  chemical  individual,  it  has  at 
once  broken  down  into  water  and  carbon  dioxide.  The 
salts  produced  by  substituting  metals  for  the  hydrogen 
of  this  acid  are,  however,  as  we  have  seen,  permanent. 
This  acid  is  termed  carbonic  acid,  and  the  salts  derived 
from  it  by  substituting  metals  for  the  hydrogen  are 
called  carbonates.  The  two  bodies  just  examined  are, 
therefore,  primary  and  secondary  potassium  carbonates. 
The  former  is  produced  by  replacing  one-half  of  the 


CARBON  DIOXIDE.  157 

hydrogen  in  a  given  quantity  of  carbonic  acid  by  the 
metal  potassium,  and  the  latter  by  replacing  all  of  the 
hydrogen  in  the  same  way.  The  learner  will  recall  in 
the  discussion  of  a  similar  case  the  primary  and  second- 
ary sulphates  (see  pages  60  and  61),  and  the  formation 
of  the  two  carbonates  of  potassium  can  be  compared  to 
the  neutralization  of  sulphuric  acid  by  potassium  hy- 
droxide. This  relationship  will  be  made  clearer  if  we 
compare  the  formulae  assigned  to  the  sulphates  of 
potassium  with  those  just  given  for  the  carbonates:  — 

KHSO4,  primary  sulphate  of  potassium. 
K2SO4,  secondary  sulphate  of  potassium. 
KHCO3,  primary  carbonate  of  potassium. 
K2CO3,  secondary  carbonate  of  potassium. 

Difference  between  the  Primary  and  Secondary  Salts  of 
Potassium.  The  primary  potassium  salts  are  those  in 
which  one  part  of  hydrogen  in  the  acids  has  been  re- 
placed by  39  parts  of  potassium,  and  the  secondary  salts 
are  those  in  which  two  parts  of  hydrogen  have  been 
replaced  by  78  (2x39)  parts  of  potassium.  The  pri- 
mary sulphate  of  potassium  is  converted  into  the  second- 
ary sulphate  (page  59)  by  the  addition  of  potassium 
hydroxide.  If  the  relationship  between  the  carbonates 
and  the  sulphates  is  to  hold  good,  it  must  therefore  fol- 
low that  the  primary  carbonates  can  be  converted  into  the 
secondary  by  similar  means.  That  this  is  the  case  can 
easily  be  shown  by  dissolving  one  gram  of  the  primary 
carbonate  in  a  little  water,  and  then  adding  .56  grams  * 

*  This  quantity,  in  centigrams,  represents  the  sum  of  the  atomic 
weights  of  potassium,  oxygen,  and  hydrogen,  which  go  to  form  potassium 
hydroxide  (see  page  145). 

potassium,  atomic  weight,  39 

oxygen,  atomic  weight,        16 

hydrogen,  atomic  weight,  _^ 

Total,  56 


158  ELEMENTS   OF  CHEMISTRY. 

of  potassium  hydroxide.*  On  evaporating  the  excess  of 
water  from  the  solution,  a  salt  will  remain,  which,  on 
addition  of  hydrochloric  acid,  gives  off  carbon  dioxide, 
but  which  does  not  evolve  that  gas  on  heating.  In 
short,  it  has  all  of  the  properties  of  the  secondary  car- 
bonate. 

The  above  change  can,  therefore,  be  represented  in  chemical 
formulae  as  follows  :  — 

KOH         +  KHCO3  K2CO8  +H2O 

Potassium  hydroxide  +  Primary  potassium  carbonate  =  Secondary  potassium  carbonate  +  Water. 
56  parts  +  100  parts  133  parts  +  18.parts. 

The  primary  carbonate  of  potassium  can,  therefore, 
be  converted  into  the  secondary  by  the  addition  of 
potassium  hydroxide,  just  as  the  primary  sulphate  is 
converted  into  the  secondary  by  the  same  means.64 

Occurrence  of  the  Carbonate  of  Potassium.  The  secondary  car- 
bonate of  potassium  occurs  as  one  of  the  constituents  of  the  ashes 
of  land  plants,  from  which  it  can  be  extracted  by  means  of  water. 
As  this  operation  was  usually  performed  in  iron  pots  or  kettles, 
the  name  potash  was  given  to  potassium  carbonate;  and  since 
potassium  hydroxide  is  prepared  from  the  latter,  the  term  caustic 
potash  was  brought  into  use  to  designate  the  hydroxide. 

Formation  of  the  Primary  and  Secondary  Carbonates  of  Sodium. 
The  sodium  carbonates  are  chemically  closely  related  to  those  of 
potassium.  If,  then,  in  the  above  reactions,  we  had  made  use  of 
sodium  hydroxide,  instead  of  potassium  hydroxide,  the  result  would 
have  been  identical ;  except  that  the  primary  and  secondary  car- 
bonates of  sodium  would  have  taken  the  place  of  those  of  potas- 
sium. The  chemical  formulae  of  these  two  substances  would 
therefore  be  Na  IICO3  and  Na2  CO3 ,  and  they  would  be  produced 
as  follows :  — 

*  This  should  be  in  the  form  of  a  solution  where  one  cubic  centimetre 
contains  .05(5  grams  of  potassium  hydroxide.  The  solution  can  be  meas- 
ured in  a  burette  (see  page  49,  and  Experiment  27  of  the  Appendix). 


C A  UK  ON  DIOXIDE.  159 

NaOH*     +       CO2       =        NaHCO3. 

Sodium  hydroxide  +  Carbon  dioxide  =  Primary  sodium  Carbonate. 
40  parts  +        44  parts  =  84  parts. 

Na  HCO3         +      Na  OH  Na  CO3  +  H2  0. 

Primary  sodium  carbonate  +  Sodium  hydroxide  =  Secondary  sodium  carbonate  +  Water. 
&i  parts  +  40  parts  =  124  parts  + 18  parts. 

Sodium  carbonate  is  commercially  more  important  than  potas- 
sium carbonate,  as  it  is  used  extensively  in  the  arts,  and  in  the 
preparation  of  soap  and  of  glass. 

Occurrences  of  Calcium  Carbonate,  Magnesium  Carbonate,  and 
Carbonate  of  Iron.  The  carbonates  of  several  other  metals  are 
extensive  and  valuable  mineral  constituents  of  the  earth's  crust. 
The  carbonate  of  calcium  occurs  in  a  massive,  not-crystalline  form, 
as  limestone,  in  blocks  formed  of  minute,  not-separable  crystals,  as 
marble,  and  in  well-formed,  often  transparent  crystals,  as  calcite, 
peculiarly  developed  forms  of  which  are  termed  Iceland  spar. 
The  shells  of  mollusks,  and  the  protective  coating  of  many  infuso- 
ria, consist  largely  of  calcium  carbonate. 

Magnesium  carbonate,  as  the  mineral  magnesite,  occurs  in  ex- 
tensive deposits.  Magnesium  and  calcium  carbonates  (dolomite) 
is  the  chief  mineral  in  a  range  of  mountains  in  the  Alps.  The 
carbonate  of  iron  is  valuable  as  an  ore. 

Preparation  of  Carbon  Dioxide  by  the  Action  of  Acids  on 
Carbonates.  All  of  the  carbonates  are  more  or  less 
readily  decomposed  by  acids.  The  result  in  each  case 
is  the  production  of  the  salt  of  the  acid  which  is  used 
with  the  metal  contained  in  the  carbonate.  At  the 
same  time  carbon  dioxide  and  water  are  formed.  We 
found  this  to  be  the  case  in  studying  potassium  carbon- 
ate, and  an  examination  of  other  carbonates  will  show 
the  same  result.  For  example,  calcium  carbonate  with 

*  NaOH  represents:  — 

One  atom  of  sodium,  atomic  weight,       23 

One  atom  of  oxygen,  atomic  weight,       16 

One  atom  of  hydrogen,  atomic  weight,    1 

Total,  40 

(See  page  143.) 


160  ELEMENTS   OF  CHEMISTRY 

hydrochloric  acid,  forms  calcium  chloride,  carbon  diox- 
ide, and  water. 

Calcium  carbonate,  in  the  form  of  marble,  can  be  easily  han- 
dled in  the  laboratory.  It  is  so  readily  attacked  by  hydrochloric 
acid  that  the  reaction  just  given  is  the  one  universally  employed 
in  preparing  carbon  dioxide  for  laboratory  use.65 

Most  Carbonates  are  Insoluble  in  Water.  Formation  of 
the  Soluble  Primary  Carbonate  of  Calcium  from  the  Insoluble 
Secondary.  The  carbonates  "of  most  metals  do  not  dis- 
solve in  water.  In  our  present  work  we  may  consider 
that  only  the  carbonates  of  potassium  and  of  sodium  are 
soluble.  As  an  illustration  we  can  show  that  if  carbon 
dioxide  is  passed  into  a  solution  of  calcium  hydroxide 
(lime-water),  the  insoluble  carbonate  of  calcium  separates 
as  a  white  powder.  If,  however,  gas  is  added  after 
the  separation  of  the  calcium  carbonate  is  completed, 
the  latter  substance  will  gradually  dissolve  in  the  ex- 
cess of  carbon  dioxide  solution,  because  the  primary 
carbonate  of  calcium  (which  is  soluble  in  water)  is  pro- 
duced by  this  means.  When  the  solution  so  formed  is 
boiled,  carbon  dioxide  passes  off,  and  the  insoluble  sec- 
ondary carbonate  of  calcium  is  again  produced.  This 
happens  because  primary  calcium  carbonate  is  less  stable 
than  primary  potassium  carbonate,  and  hence  it  decom- 
poses at  a  lower  temperature.  This  change  is  parallel 
to  the  decomposition  of  primary  potassium  carbonate 
by  heat,  which  we  studied  at  the  beginning  of  this 
chapter.66 

Occurrence  of  the  Primary  Calcium  Carbonate  in  Spring  and  River 
Water.  Owing  to  the  action  of  carbon  dioxide  on  the  carbonate 
of  calcium,  which,  in  the  form  of  mineral  deposits,  constitutes  a 
large  portion  of  the  beds  of  springs  and  rivers,  part  of  the  lime- 
stone is  dissolved  as  primary  calcium  carbonate.  Water,  which 


CARBON  DIOXIDE.  161 

contains  this  substance  in  solution,  will,  when  boiled,  deposit  sec- 
ondary calcium  carbonate  on  the  walls  of  the  kettle.  This  phe- 
nomenon is  always  observed  where  hard  water  is  boiled.  In 
addition  to  the  primary  calcium  carbonate,  calcium  sulphate, 
which  is  also  slightly  soluble  in  water,  is  generally  found  in 
spring  and  river  water.  This  substance  is  not  separated  by  boil- 
ing. Waters  which  contain  either  primary  calcium  carbonate,  or 
calcium  sulphate,  or  both,  are  termed  hard  waters.  Those  which 
have  only  primary  calcium  carbonate  are  temporary  hard  waters, 
for  this  constituent  can  be  removed  by  boiling;  those  which 
contain  calcium  sulphate  are  permanent  hard  waters. 

Summary. 

1.  When  carbon  is  burned  in  the  air,  carbon  dioxide 
is  produced. 

2.  Carbon  dioxide,  in  each  molecule,   contains  one 
atom   of  carbon   and  two   of  oxygen.     Its   formula  is 
C02. 

3.  Carbon  dioxide  is  absorbed  by  potassium  hydrox- 
ide.    When  a  solution  of  potassium  hydroxide  is  com- 
pletely saturated  by  carbon  dioxide,  it  contains  primary 
potassium  carbonate,  the  formula  of  which  is  KHCO3. 

4.  When    the    primary   carbonate    of   potassium   is 
heated,  or  when  potassium  hydroxide  is  added  to  it,  it 
is  changed  into  the  secondary  carbonate  of  potassium, 
the  formula  of  which  is  K2  CO3 .     There  is  also  a  pri- 
mary and  a  secondary  carbonate   of  sodium  to  which 
respectively  the  formulae  Na  HCO3  and  Na2  CO3  can  be 
assigned. 

5.  The  carbonates  of  a  number  of  other  metals  (cal- 
cium,  magnesium,   iron)   form    extensive    mineral    de- 
posits.    These  carbonates  are  insoluble  in  water,  while 
those  of  potassium  and  sodium  are  soluble.     The  car- 
bonates, on  addition  of  acids,  liberate  carbon  dioxide. 


162  ELEMENTS   OF  CHEMISTRY. 

6.  The  primary  carbonates  are  all  soluble  in  water. 
The    above    insoluble    minerals    are,    therefore,    partly 
brought  into  solution  by  the  combined  action  of  water 
and  the  dissolved  carbon  dioxide. 

7.  When  the  water  containing  them  is  boiled,  these 
primary  carbonates  are  decomposed,  and  the  insoluble 
secondary    carbonates    are    deposited.      From    primary 
calcium  carbonate  in  temporary  hard  water,  a  deposit 
of  secondary  calcium  carbonate  is  produced. 


CARBON  MONOXIDE  AND  METHANE.  163 


CHAPTER 


CARBON     MONOXIDE     AND     METHANE 
(HYDROGEN     CARBIDE). 

THE  second  oxide  of  carbon  is  carbon  monoxide. 
This  gas  is  easily  produced  by  taking  away  a  portion  of 
the  oxygen  from  carbon  dioxide. 

Preparation  and  Properties  of  Carbon  Monoxide.  If  carbon  diox- 
ide is  passed  through  an  iron  tube  containing  pieces  of  charcoal 
heated  to  redness,  and  then  into  bottles  rilled  with  water  and  in- 
verted over  a  vessel  filled  with  the  same  liquid,  the  gas  collected 
will  differ  from  carbon  dioxide.  It  will  not  be  absorbed  by  the 
potassium  hydroxide  as  carbon  dioxide  is  ;  it  will  burn  in  the  air 
when  a  lighted  taper  is  applied  to  the  mouth  of  the  jar  containing 
it  ;  and  it  is  scarcely  soluble  in  water.  This  new  gas  is  termed 
carbon  monoxide.  It  is  intensely  poisonous.  Its  specific  gravity 
(hydrogen  =  2)  is  28,  its  molecular  weight  (H2  =  2)  is  also  28. 
In  28  parts  there  are  12  of  carbon  and  16  of  oxygen.  These 
numbers,  as  we  have  seen,  represent  the  relative  atomic  weights 
of  carbon  and  oxygen  respectively,  so  that  one  molecule  of  carbon 
monoxide  contains  one  atom  of  carbon  and  one  of  oxygen.  Its 
structure  can  therefore  be  represented  by  the  formula  CO.67 

Reduction.  The  process  of  taking  away  oxygen  from 
carbon  dioxide  to  form  carbon  monoxide  is  the  reverse 
of  the  oxidation  by  which  carbon  monoxide  is  converted 
into  carbon  dioxide.  Such  a  process,  in  chemical  lan- 
guage, is  termed  reduction. 

Change  in  Energy  when  Carbon  Monoxide  burns  to  form 
Carbon  Dioxide.  When  carbon  monoxide  burns,  a  large 


164  ELEMENTS   OF  CHEMISTRY. 

amount  of  heat  is  given  off.  The  carbon  dioxide  pro- 
duced, therefore,  possesses  less  chemical  energy  than 
the  monoxide.  We  can  determine  the  total  amount  of 
heat  evolved  in  burning  a  given  weight  of  carbon.  We 
can  also  ascertain  the  total  heat  produced  when  carbon 
monoxide,  containing  the  same  weight  of  carbon,  is  con- 
verted into  carbon  dioxide.  The  difference  between 
these  two  quantities  must  necessarily  give  us  the  heat 
given  off  in  forming  the  equivalent  amount  of  carbon 
monoxide.*  By  this  means  it  has  been  ascertained 
that  carbon,  in  being  partially  oxidized  to  carbon  mon- 
oxide, gives  off  kinetic  energy,  and  that  the  resulting 
gas  contains  less  chemical  energy  than  did  its  original 
constituents,  carbon  and  oxygen.  Furthermore,  carbon 
monoxide,  in  burning  to  carbon  dioxide,  again  gives  off 
energy.  The  energy  changes  attending  the  formation 
of  carbon  dioxide  can,  therefore,  be  considered  as 
taking  place  in  two  stages ;  but  the  total  amount  of 
kinetic  energy  evolved  when  a  given  weight  of  carbon 
burns  to  carbon  dioxide  is  the  same  as  if  the  same 
amount  were  first  changed  to  carbon  monoxide  and  then 
to  carbon  dioxide.  The  total  kinetic  energy  manifested 
during  a  chemical  change  is,  therefore,  independent  of 
the  intermediary  bodies  which  may  be  formed.  This  is 
exactly  the  case  with  a  weight  which  is  allowed  to  fall 
from  a  certain  height  to  the  ground.  The  total  energy 
given  off  is  obviously  the  same,  no  matter  whether  it  Jbe 
allowed  to  descend  without  interruptions,  or  whether  it 
be  stopped  at  intervals..  It  will  obviously  require  the 
same  amount  of  energy  to  bring  it  back  to  its  original 
position,  no  matter  what  were  the  circumstances  attend- 
ing its  fall. 

*  I.e.,  the  amount  of  carbon  monoxide  containing  the  above  given 
weight  of  carbon. 


CARBON  MONOXIDE  AND  METHANE.  165 

Far  more  important  than  carbon  monoxide,  for  the 
purposes  of  our  present  work,  is  the  hydrogen  com- 
pound of  carbon  which  is  known  as  methane,  or  hydro- 
gen carbide. 

Methane;  Natural  Occurrence  and  Formation.  Hydrogen  and 
carbon  cannot  be  brought  to  unite  directly  except  with  the  great- 
est difficulty,  and  then  only  irl  the  smallest  quantity.  In  this  re- 
spect carbon  resembles  nitrogen  (see  page  88).  It  is  not  difficult, 
however,  to  produce  methane  from  other  compounds  which  con- 
tain both  carbon  and  hydrogen.  For  example,  it  is  constantly 
formed  at  the  bottom  of  swamps  and  stagnant  pools  where  vege- 
table matter  (largely  made  up  of  the  two  elements  in  question) 
is  decaying  under  the  influence  of  micro-organisms,  and  where 
the  amount  of"  oxygen  required  for  a  complete  decomposition  is 
not  accessible.  The  methane  produced  by  these  processes  of 
decay  passes  off  in  the  form  of  bubbles,  the  number  of  which  can 
be  increased  by  stirring  the  bottom  of  the  pool  with  a  stick.  It 
is  owing  to  the  above  origin  that  methane  is  frequently  termed 
"  marsh  gas."  Natural  marsh  gas  is  contaminated  with  carbon 
dioxide  and  nitrogen.  The  "  natural  gas,"  which  escapes  freely 
from  borings  in  many  localities,  consists  largely  of  methane, 
which  probably  found  its  origin  in  the  decomposition  of  vegetable 
matter  buried  in  past  geologic  eras.  The  remains  of  this  now 
constitute  bituminous  and  anthracite  coal.  Owing  to  similar 
reasons,  methane  frequently  occurs  in  coal-mines. 

Preparation  of  Methane  for  Laboratory  Purposes.  In  preparing 
methane  for  laboratory  purposes,  we  have  to  make  use  of  a  corn- 
pound  known  as  sodium  acetate,  with  the  exact  constitution  of 
which  we  need  not  at  present  be  acquainted.  It  is  sufficient  for 
our  purposes  to  know  that  it  is  formed  of  carbon,  hydrogen,  oxy- 
gen, and  sodium,  and  that,  when  heated  in  the  presence  of  a  mix- 
ture of  sodium  hydroxide  and  calcium  oxide,  it  separates,  in  the 
form  of  methane,  a  portion  of  the  carbon  and  all  of  the  hydrogen 
which  it  contains.68 

Properties  of  Methane.  Methane  is  a  gas,  colorless,  odorless, 
and  tasteless.  If  a  jar  of  it  is  collected  over  water,  and  a  lighted 


166  ELEMENTS   OF  CHEMISTRY. 

taper  is  applied  to  the  jar,  which  has  been  removed -from  the 
water  and  held  mouth  downward,  we  shall  find  that  the  gas  burns 
with  a  nearly  non-luminous  flame.  This  flame  greatly  resembles 
that  of  hydrogen,  but,  nevertheless,  can  be  distinguished  from  it 
because  the  hydrogen  flame  is  entirely  non-luminous.  The  spe- 
cific gravity  of  methane  is  less  than  that  of  air.  This  can  easily 
be  shown  by  filling  two  cylinders  with  methane,  and  holding  one 
mouth  upward  and  the  other  mouth  downward  for  a  few  seconds. 
The  former  will  no  longer  contain  a  combustible  gas,  for  its 
methane  will  have  risen  into  the  air.  The  latter  will  have  re- 
tained all  its  methane,  and  if  a  lighted  taper  is  applied,  will  show 
the  characteristic  flame  of  that  substance.  Methane  is  nearly 
insoluble  in  water.69 

Determination  of  the  Chemical  Formula  of  Methane.  In 
determining  the  chemical  formula  of  methane,  we  can- 
not have  so  easy  a  task  as  we  did  when  engaged  in 
similar  studies  with  hydrogen  chloride,  water,  or  am- 
monia. Both  constituents  entering  into  the  formation 
of  each  of  the  latter  compounds  are  gases,  and  for  that 
reason  a  study  of  the  uniting  gas  volumes  together 
with  the  fundamental  theory  that  in  equal  volumes  of 
gases  there  are  equal  numbers  of  molecules,  directly 
led  us  to  the  structure  of  those  three  substances,  and 
thence  to  the  formulae,  HC1,  H2O,  and  NH3.  In 
methane,  however,  one  of  the  constituent  elements 
(carbon)  is  a  solid  under  any  conditions  which  we  can 
command.  Therefore,  any  view  which  may  be  held  as 
to  the  relative  volume  of  that  element  entering  into  the 
formation  of  the  gas  cannot  be  based  upon  direct  meas- 
urement. It  must  be  established  both  by  reasoning 
from  our  experience  with  the  other  hydrogen  com- 
pounds (hydrochloric  acid,  water,  and  ammonia),  and 
by  noting  chemical  changes  to  which  we  can  subject 
methane. 


CARBON  MONOXIDE  AND  METHANE.     167 

Previous  experience  has  shown  us  that  we  have  three 
kinds  of  gaseous  hydrogen  compounds  of  the  not-metals 
which,  we  may  say,  belong  to  three  distinct  types.  The 
first  of  these,  hydrogen  chloride,  is  produced  by  the 
union  of  ^one  volume  of  hydrogen  with  one  volume  of 
chlorine,  the  second  by  the  union  of  two  volumes  of 
hydrogen  with  one  volume  of  oxygen,  and  the  third 
by  the  union  of  three  volumes  of  hydrogen  with  one 
volume  of  nitrogen.  In  each  of  these  cases  one  volume 
of  the  not-metal  is  united  with  one  or  more  volumes  of 
hydrogen.  If  methane  is  a  compound  which  is  at  all 
parallel,  it  seems  reasonable  to  suppose  that  it  contains 
one  volume  of  carbon  united  with  one  or  more  volumes 
o£  hydrogen.  This  volume  of  hydrogen  is  consequently 
to  be  ascertained  by  chemical  changes  to  which  we  can 
subject  methane. 

Volumetric  Composition  of  Methane  by  Explosion  with 
Oxygen.  When  methane  burns  in  oxygen  it  produces 
carbon  dioxide  and  water.  This  fact  gives  us  a  means 
of  ascertaining  the  volume  of  hydrogen  which  is  con- 
tained in  one  volume  of  methane. 

Introduce  about  ten  cubic  centimetres  of  methane  into  a  eudi- 
ometer tube  over  mercury,  and  then  admit  omewhat  more  than 
twice  this  volume  of  pure  oxygen.  Heat  the  eudiometer  to  the 
temperature  of  boiling  water  by  means  of  a  steam-jacket  (see  page 
26,  and  Experiment  11  of  Appendix),  and  explode  the  gas  mixture 
by  an  electric  spark,  exactly  as  was  done  in  the  study  of  the  com- 
bining volumes  of  oxygen  and  hydrogen.  If  all  due  precautions 
have  been  taken,  it  will  be  found  that  no  change  in  the  total  volume 
takes  place  when  methane  and  oxygen  are  converted  into  carbon 
dioxide  and  water.  There  are  consequently  as  many  molecules 
of  carbon  dioxide  and  water  produced  as  there  were  molecules  of 
methane  and  oxygen  before  the  explosion.  If,  now,  the  whole 
apparatus  is  allowed  to  cool,  the  water  vapor  will  be  changed  to  a 


168  ELEMENTS   OF  CIIEMISTItY. 

liquid,  so  that  its  volume  can  be  neglected  in  the  subsequent  cal- 
culation. As  the  water  condenses,  the  mercury  will  rise,  owing  to 
the  contraction  of  the  total  gas  volume,  and,  when  its  position  is 
constant,  there  will  have  been  exactly  twenty  cubic  centimetres 
diminution.  These  twenty  cubic  centimetres  must  therefore 
represent  the  volume  of  water  vapor  which  was  formed  from  ten 
cubic  centimetres  of  methane.*  If  a  very  small  piece  of  caustic 
potash  is  now  introduced  at  the  bottom  of  the  tube,  it  will  rise  to 
the  top  of  the  mercury,  and  absorb  the  carbon  dioxide  which  was 
produced  by  the  explosion,  so  that  a  further  contraction  will  take 
place.  This  latter  will  be  exactly  ten  cubic  centimetres,  which  is 
equal  to  the  volume  of  methane  originally  present.  The  gas 
which  finally  remains  is  oxygen,  and  represents  the  excess  of  that 
substance  which  was  added.  The  results  of  the  above  measure- 
ments can  be  tabulated  as  follows  :  — 

1.  Volume  of  methane  =10  cubic  centimetres. 

2.  Volume  of  gases  at  100°  before  and  after  the  explosion, 
unaltered. 

3.  Contraction,  owing  to  condensation  of  water  vapor,  20  cubic 
centimetres. 

4.  Contraction,  owing  to  the  absorption  of   carbon  dioxide, 
10  cubic  centimetres. 

Volume  of  methane  =  10  cubic  centimetres. 
Volume  of  water  vapor  =  20  cubic  centimetres. 
Volume  of  carbon  dioxide  =10  cubic  centimetres. 
As  a  final  result,  therefore,  we  find  the  following  — 


*  Of  course  the  above  description  presupposes  that  all  the  volumes 
mentioned  have  been  calculated  to  0°  and  760  mm.  pressure.  In  actual 
practice  the  height  of  the  barometer,  the  temperature,  the  height  of  the 
column  of  mercury  in  the  eudiometer  tube,  and  the  volume  of  gas  in  the 
cube,  must  be  noted  at  the  following  stages  of  the  experiment:  1.  After 
admitting  the  methane.  2.  After  admitting  the  oxygen.  3.  After  ex- 
ploding the  gas  mixture  (this  volume  is  at  100°).  4.  After  allowing  the 
products  of  the  explosion  to  cool.  In  this  instance  the  tension  of  water 
vapor  must  be  taken  into  account,  as  at  this  point  the  water  pi-oduced  by 
the  explosion  is  present  as  such.  5.  After  introducing  the  piece  of 
caustic  potash.  The  calculation  for  the  tension  of  water  vapor  here  dis- 
appears, for  the  caustic  potash  will  absorb  the  water  which  is  present. 
See  pages  68,  69,  and  70. 


CARBON  MONOXIDE  AND  METHANE.  169 

Results  of  the  Explosion  of  Methane  with  Oxygen.      One 

volume  of  methane,  when  exploded  with  oxygen,  produces 
one  volume  of  carbon  dioxide  and  two  volumes  of  water 
vapor.  As  in  equal  volumes  of  gases  there  are  equal 
numbers  of  molecules,  this  result  means  that  one  mole- 
cule of  methane  produces  one  molecule  of  carbon  dioxide 
and  two  molecules  of  water.  Now  we  have  decided  that 
two  molecules  of  water  must  contain  four  atoms  of 
hydrogen;  and  since  these  four  atoms  of  hydrogen 
have  been  furnished  by  one  molecule  of  methane,  it 
must  follow  that  — 

One  molecule  of  methane  contains  four  atoms  of  hy- 
drogen. 

We  have  also  come  to  the  conclusion  that  one  mole- 
cule of  carbon  dioxide  contains  one  atom  of  carbon  (see 
page  154);  and,  since  this  one  atom  of  carbon  must 
have  been  furnished  by  one  molecule  of  methane,  it 
follows  that  — 

One  molecule  of  methane  contains  one  atom  of  carbon. 

Combining  these  two  results  we  find  that:  — 

One  molecule  of  methane  is  composed  of  one  atom 
of  carbon  and  four  atoms  of  hydrogen.  Therefore  its 
formula  is  represented  by  CH4.70 

Formula  of  Methane  from  a  Consideration  of  its  Specific 
Gravity.  This  conclusion  as  to  the  formula  of  methane 
is  borne  out  by  its  specific  gravity,  which  is  16  (hydro- 
gen =  2).  The  molecular  weight  of  methane  (H2  =  2) 
is  consequently  16  ;  and  in  16  parts  of  methane  we  find, 
on  analysis,  twelve  of  carbon  and  four  of  hydrogen. 
In  working  with  carbon  dioxide  we  decided  that  12 
represented  the  relative  weight  of  one  atom  of  carbon 
measured  by  the  standard  of  one  atom  of  hydrogen. 


170  ELEMENTS   OF  CHEMISTRY. 

For  the  same  reason  4  represents  four  times  the  weight 
of  one  atom  of  hydrogen ;  so  that,  judging  from  the 
specific  gravity  of  methane,  its  structure  is  such  as 
would  be  produced  by  the  union  of  one  atom  of  carbon 
with  four  of  hydrogen ;  thus  its  formula  is  CH4 . 

Summary. 

1.  Carbon  monoxide  can  be  produced  by  the  reduc- 
tion of  carbon  dioxide. 

2.  When  carbon  monoxide  burns,  carbon  dioxide  is 
produced,  heat  is  given  off.     Therefore  carbon  dioxide 
possesses  less  chemical  energy  that  carbon  monoxide. 

3.  The  energy  changes  attending  the  formation  of 
carbon  dioxide  can  be   considered  as  taking  place  in 
two  stages,  the  first  corresponding  to  the  formation  of 
carbon  monoxide,   and   the  second  to  the    conversion 
of  carbon  monoxide  into  carbon  dioxide. 

4.  The  total  kinetic  energy  manifested  during  the 
conversion   of  a  given  weight  of  carbon  into   carbon 
dioxide  is  independent  of  any  intermediary  formation 
of  carbon  monoxide. 

5.  The    hydrogen    compound    of    carbon,    which    is 
termed  methane,  is  produced  in  nature  by  the  decom- 
position of  vegetable  matter  protected  from  the  direct 
action  of  the  air. 

6.  The    chemical    formula    of    methane    cannot    be 
directly  determined  from  combining  gas  volumes,  first, 
because  carbon  is  not  a  gas,  and  second,  because  the  ele- 
ments carbon  and  hydrogen  do  not  easily  unite  directly. 

7.  The  formula  of  methane  can  be   ascertained  by 
exploding  the  gas  with  oxygen  and  then  measuring  the 
volume  of  water  vapor  and  of  carbon  dioxide  which  is 
produced  by  this  means. 


CAB  13 ON  MONOXIDE  AND  METHANE.          171 

8.  One    volume    of   methane,   under   these    circum- 
stances, produces  one  volume   of  carbon  dioxide  and 
two  volumes  of  water  vapor.     Hence,  one  molecule  of 
methane  produces  one  molecule  of  carbon  dioxide  and 
two  molecules  of  water. 

9.  One    molecule    of    carbon    dioxide    contains    one 
atom  of  carbon,  and  two  molecules  of  water  contain 
four  atoms  of  hydrogen.     Hence,  methane  contains  one 
atom  of  carbon  to  every  four  atoms  of  hydrogen. 

10.  Methane  contains  one  atom  of  carbon  and  four 
atoms  of  hydrogen  in   each   molecule,   for  its   specific 
gravity  (hydrogen  =  2)   is   16.     Hence   its  molecular 
weight  is  16.     Such  a  molecular  weight  is   equal  to 
the  sum  of  the  atomic  weights  of  one  atom  of  carbon 
(12),  and  four  atoms  of  hydrogen  (4).     Therefore  the 
formula  for  one  molecule  of  methane  is  CH4. 


172  ELEMENTS   OF  CHEMISTRY. 


CHAPTER   XXII. 

SUBSTITUTION   OF   HYDROGEN  IN  METHANE 
BY   CHLORINE. 

Substitution  of  Hydrogen  by  Metals.  We  have  learned 
in  discussing  the  hydrogen  compounds  which  preceded 
methane,  that  certain  metals  could  replace  a  portion, 
or  all,  of  the  hydrogen  in  those  compounds.  This 
process,  which  was  general  with  all  but  methane,  we 
termed  substitution.  We  also  learned  that  the  same 
kind  of  substitution  takes  place  when  metals  act  on 
acids.  Therefore  salts  were  considered  as  being  the 
acids  in  which  a  portion,  or  all,  of  the  hydrogen  had 
been  replaced  by  other  metals.  If  we  have  carefully 
observed  all  the  phenomena  attending  the  substitution 
of  hydrogen  in  hydrogen  chloride,  water,  and  ammonia 
by  metals,  we  shall  have  noticed  that  the  ease  with 
which  the  hydrogen  is  so  replaced,  and  the  number  of 
metals  capable  of  entering  into  such  substitutions,  di- 
minishes as  we  pass  from  hydrogen  chloride  to  water, 
and  from  water  to  ammonia.  Finally,  in  methane  we 
have  a  hydrogen  compound  which,  under  ordinary  cir- 
cumstances, is  entirely  indifferent  to  metals.  Sodium, 
for  example,  can  be  left  in  contact  with  pure,  dry 
methane  for  any  length  of  time  without  suffering  the 
slightest  alteration. 

Difference  between  the  Action  of  Chlorine  and  of  the 
Metals.  On  the  other  hand,  we  have  a  radically  differ- 


SUBSTITUTION  OF  HYDROGEN  IN  METHANE.      173 

ent  behavior  toward  chlorine.  Chlorine,  of  course,  has 
no  effect  on  hydrogen  chloride ;  but  when  we  dissolved 
chlorine  in  water,  and  exposed  the  solution  to  the  sun- 
light, we  saw  that  hydrochloric  acid  was  formed  and 
oxygen  was  liberated  (see  page  44),  while  with  am- 
monia and  chlorine  we  produced  hydrogen  chloride  and 
nitrogen  (see  page  92).  In  each  instance,  then,  chlorine 
liberated  the  not-metal  which  was  present  in  the  hydro- 
gen compound,  while  it  itself  appropriated  the  hydrogen. 
Obviously  these  reactions  could  not  be  compared  with 
substitution.  It  is  now  in  order  to  study  the  action  of 
chlorine  on  methane. 

Action  of  Chlorine  on  Methane.  Two  glass  jars  of  equal  size  are 
taken,  one  filled  with  chlorine,  the  other  with  methane.  A  glass 
cover  is  placed  on  each  so  that  no  gas  can  escape.  ^  The  mouths 
are  then  brought  together,  the  glass  coverings  are  removed,  and 
the  chlorine  and  methane  are  intimately  mixed  by  inverting  the 
jars  once  or  twice,  while  their  mouths  are  held  tightly  to- 
gether.* 

If,  now,  a  lighted  taper  is  applied  to  one  of  the  vessels,  the  mix- 
ture of  gases  will  burn,  dense  fumes  of  hydrogen  chloride  will  be 
given  off,  while  carbon  will  separate  from  the  methane  in  the 
form  of  soot.  Under  the  circumstances  which  have  been  out- 
lined, methane  acts  toward  chlorine  just  as  water  and  ammonia 
do,  —  carbon  is  separated,  while  the  chlorine  appropriates  the  hy- 
drogen to  form  hydrogen  chloride.  An  entirely  different  result, 
however,  is  obtained  if  chlorine  and  methane  are  allowed  to  act 
upon  each  other  gradually.71 

For  this  purpose  the  apparatus  can  be  used  which 
was  employed  to  demonstrate  that  equal  volumes  of 
ammonia  and  hydrogen  chloride  unite  to  form  ammo- 
nium chloride  (see  Experiment  55  of  the  Appendix). 

*  This  operation  must  be  conducted  in  a  dimly  lighted  room,  and  not 
in  the  sunlight. 


174  ELEMENTS   OF  CHEMISTRY. 

One  of  the  two  equal  tubes  is  carefully  filled  with  pure  chlorine, 
the  other  with  methane,  and  the  tips  are  sealed.  The  apparatus 
is  placed  in  strong  daylight,  and  the  two  gases  are  allowed  to 
mingle  slowly.  After  some  days  the  color  of  the  chlorine  will 
entirely  disappear.  If,  now,  one  of  the  tips  is  broken  off  under  a 
solution  of  blue  litmus,  the  liquid  will  rise  in  the  apparatus  until 
exactly  one-half  is  filled,  while  the  litmus  will  turn  from  blue 
to  red,  showing  that  an  acid  is  present.  This  acid  can  easily 
be  shown  to  be  hydrochloric  acid.*  If  the  upper  tip  of  the  tube 
is  now  broken  off,  and  the  whole  lowered  into  the  litmus  solution 
so  as  to  produce  a  slight  pressure,  the  escaping  gas  can  be  ignited. 
It  will  burn  with  a  greenish  flame  entirely  different  from  that 
of  pure  methane.  This  flame  is  characteristic  of  burning  com- 
pounds of  carbon,  hydrogen,  and  chlorine.  The  explanation  of 
the  above  experiment  is  simple.  The  volume  of  methane  .reacted 
with  an  equal  volume  of  chlorine  to  produce  one  volume  of  the 
new  chlorinated  gas.  The  hydrogen  chloride  which  was  formed 
at  the  same  time,  and  which  is  readily  soluble  in  water,  was 
absorbed  by  the  litmus  solution.  It  is,  therefore,  evident  that 
one  volume  of  methane  with  one  volume  of  chlorine  produced  one 
volume  of  the  new  gas  and  one  volume  of  hydrogen  chloride. 
Therefore,  one  molecule  of  methane  with  one  molecule  of  chlo- 
rine formed  one  molecule  of  hydrogen  chloride  and  one  molecule 
of  chlorinated  methane.  As  one  molecule  of  chlorine  contains 
two  atoms  of  that  element,  the  change  can  be  represented  as 
follows :  — 72 

CH4       +     C1C1      =    CH3C1    +  HC1. 

One  mol.  of  methane  4-  Onemol.  of  chlorine  =  One  mol.  of new  gas  +  Oneniol.  of  hydrogen  chloride. 

The  First  Product  of  the  Action  of  Chlorine  on  Methane 
is  Methyl  Chloride.  The  new  gas  which  is  produced  is 
called  methyl  chloride.  It  is  methane  in  each  molecule 
of  which  one  atom  of  hydrogen  has  been  replaced  (sub- 
stituted) by  one  atom  of  chlorine.  It  is  evident,  there- 
fore, that  if  chlorine  is  allowed  to  act  slowly  on  methane, 

*  By  adding  a  solution  of  silver  nitrate  to  the  litmus  solution,  the  in- 
soluble chloride  of  silver  will  be  produced,  thus  indicating  the  presence 
of  hydrochloric  acid. 


SUBSTITUTION   OF  HYDROGEN   IN  •METHANE.      1 

substitution  takes  place,  and  that  the  chTo'niie'^vrmch  is 
introduced  takes  the  place  of  the  hydrogen  which  has 
been  expelled. 

Chlorination  of  Methyl  Chloride.  The  operation  of  substitution 
can  be  carried  still  farther  if,  when  the  hydrogen  chloride  has 
been  removed  by  means  of  the  litmus  solution,  one  arm  of  the  tube 
containing  methyl  chloride  (after  the  action  of  chlorine  on  meth- 
ane) is  not  opened.  Close  the  stopcock  separating  the  two  halves 
of  the  apparatus,  and  drain  off  the  water  contained  in  the  lower 
half.  Fill  this  again  with  chlorine  and  seal  it,  allowing  the  gases 
to  mix  as  in  the  first  instance.  The  phenomena  previously  observed 
will  be  repeated  ;  i.e.,  the  color  of  the  chlorine  will  disappear,  and, 
when  the  tube  is  opened  under  a  litmus  solution,  it  will  be  found 
that  one  volume  of  hydrogen  chloride  and  one  volume  of  a  chlo- 
rinated methhl  chloride  will  have  been  formed.  From  this  it  fol- 
lows that  one  molecule  (volume)  methyl  chloride  with  one  molecule 
(volume)  of  chlorine  produces  one  molecule  (volume)  of  hydrogen 
chloride  and  one  molecule  (volume)  of  chlorinated  methane.  This 
second  change  can  be  represented  as  follows  :  — 73 

CH3C1  +      C1C1       =   CH2C12    +  HC1. 

1  mol.  methyl  chloride  +1  mol.  chlorine  =  1  mol.  new  gas  +  1  mol.  hydrogen  chloride. 

The  Second  Product  of  the  Action  of.  Chlorine  on  Methane 
is  Methylen  Chloride.  The  second  chlorinated  gas  which 
is  produced  is  called  methylen  chloride.  It  is  methane 
in  each  molecule  of  which  two  atoms  of  hydrogen  have 
been  replaced  (substituted)  by  two  atoms  of  chlorine. 

Chlorination  of  Methylen  Chloride.  Methylen  chloride  is  also 
capable  of  reacting  with  chlorine,  but  in  this  instance  we  cannot 
easily  measure  the  gas  volume  produced.  The  reason  is  that  the 
third  substitution  product  of  methane  is  a  liquid  at  ordinary  tem- 
peratures, so  that  on  opening  the  tube  under  water,  the  latter  will 
rush  in  and  entirely  fill  the  apparatus,  except  the  very  small  space 
occupied  by  the  substitution  product.  We  will  soon  see,  however, 
that  by  a  careful  study  of  the  specific  gravity  of  the  vapor  of  the 
liquid  formed,  we  can  ascertain  that  this  substitution  has  pro- 
ceeded like  the  others,  and  that  — 


176  ELEMENTS   OF  CHEMISTRY. 

One  molecule  of  methylen  chloride,  with  one  molecule  of  chlo- 
rine, has  produced  one  molecule  of  the  new  substitution  product, 
together  with  one  molecule  of  hydrogen  chloride.  This  change 
can  be  represented  as  follows  :  — 74 

CH2C12      +  C1C1   =      CHC13      +        HC1. 

1  mol.  methylen  chloride  +  1  mol.  chlorine  =  1  mol.  of  the  new  product  + 1  mol.  hydrogen  chloride 

The  Third  Product  of  the  Action  of  Chlorine  on  Methane 
is  Methin  Chloride,  and  the  Fourth,  Carbon  Tetrachloride. 
The  third  substitution  product  of  methane  is  methin 
chloride,  commonly  known  as  chloroform.  If  chloro- 
form is  subjected  to  the  continued  action  of  chlorine, 
the  last  remaining  hydrogen  atom  in  each  molecule 
will  be  substituted,  and  we  shall  finally  have  a  methane 
in  which  all  the  hydrogen  has  been  replaced  by  chlo- 
rine. This  last  methane  is  called  carbon  tetrachloride. 
It  is  a  liquid  at  ordinary  temperatures,  but  can  easily 
be  converted  into  a  gas. 

Specific  Gravities  and  Boiling-Points  of  Methane  and  its 
Substitution  Products.  It  is  most  instructive  to  compare 
the  specific  gravities  of  methane  and  of  its  chlorine 
substitution  products,  when  all  five  substances  have 
been  heated  to  a  temperature  sufficient  to  convert  them 
into  gases.  That  this  is  easily  accomplished  will  be 
seen  from  a  table  giving  their  boiling-points. 

Methane  boils  at   ....     ...."- 164°. 

Methyl  chloride  boils  at       ....       -   23  .7°. 

Methylen  chloride  boils  at  .     .     .     .     +  40°. 

Methin  chloride  (chloroform)  boils  at   +  61°. 
Carbon  tetrachloride  boils  at  .     .     .     +  76°. 

Since  all  these  compounds  are  gases  at  temperatures 
below  the  boiling-point  of  water  (100°)  their  specific 
gravities  as  vapors  can  easily  be  ascertained.  These 
specific  gravities  are  given  in  the  following  table :  — 


SUBSTITUTION  OF  HYDROGEN  IN  METHANE.      177 

Specific  gravities  of  methane  and  its  substitution  products  as  gases. 
Hydrogen  =  2 

Methane,  specific  gravity  16,  molecular  weight  16,  contains  12 
parts  of  carbon  and  4  of  hydrogen. 

Methyl  chloride,  specific  gravity  50.5,  molecular  weight  50.5,  con- 
tains 12  parts  of  carbon,  3  of  hydrogen,  and  35.5  of  chlorine. 

Methylen  chloride,  specific  gravity  85,  molecular  weight  85,  con- 
tains 12  parts  of  carbon,  2  of  hydrogen,  and  71  of  chlorine. 

Methin  chloride,  specific  gravity  119.5,  molecular  weight  119.5, 
contains  12  parts  of  carbon,  1  of  hydrogen,  and  106.5  of 
chlorine. 

Carbon  tetrachloride,  specific  gravity  154,  molecular  weight  154, 
contains  12  parts  of  carbon  and  142  parts  of  chlorine. 

Atomic  Weights  of  Carbon  and  Chlorine  as  ascertained 
from  the  Specific  Gravities  of  Methane  and  the  Chlorinated 
Methanes.  The  figures  in  this  table  furnish  additional 
proof  that  the  weight  of  an  atom  of  carbon  is  twelve 
times  that  of  an  atom  of  hydrogen,  since  we  have  here 
five  compounds,  each  containing  12  parts  of  carbon 
in  every  molecule.  The  atomic  weight  of  carbon 
cannot,  therefore,  be  more  than  12.  That  it  is  not 
less  than  this  number  is  rendered  more  probable  the 
more  gaseous  compounds  of  carbon  are  investigated, 
since  each  will  be  shown  to  contain  not  less  than  12 
parts  of  that  element  in  every  molecule.  Furthermore, 
it  is  evident  that  the  relative  atomic  weight  of  chlorine 
cannot  be  a  multiple  of  35.5,  because  we  have  one  of 
the  above  compounds  (methyl  chloride)  which  contains 
but  35.5  parts  of  chlorine  in  each  molecule.  It  follows 
from  this  that  methylen  chloride,  methin  chloride,  and 
carbon  tetrachloride  contain,  in  each  molecule,  two, 
three,  and  four  atoms  of  chlorine  respectively.  Rea- 
soning from  the  specific  gravities  of  methane  and  of 
the  chlorinated  methanes,  when  those  substances  are 


178  ELEMENTS   OF  CHEMISTRY. 

converted  into  gases,  we  must  come  to  the  conclusion 
that  their  molecules  have  the  formulae  CH4,  CH3  Cl, 
CH2  C12,  CH  C13,  and  C  C14. 

In  Substituting  Hydrogen  by  Chlorine,  the  Essential 
Character  of  Methane  is  not  changed.  In  substituting 
hydrogen  by  chlorine  in  methane,  the  essential  char- 
acter of  the  latter  is  preserved.  All  the  chlorinated 
compounds  contain  one  atom  of  carbon  in  each  mole- 
cule. The  hydrogen  has  been  substituted  while  the 
carbon  has  remained.  It  seems  reasonable  to  suppose, 
therefore,  that  in  a  molecule  of  methane,  it  is  the 
carbon  atoms  which  hold  the  four  hydrogen  atoms  in 
chemical  union  with  it.  In  producing  the  chlorine  sub- 
stitution products,  the  substituting  chlorine  atoms  have 
taken  the  place  of  the  hydrogen  atoms  which  are  sub- 
stituted. We  can  express  this  conclusion  in  the  fol- 
lowing way:  - 

The  Number  of  Atoms  with  which  one  Atom  of  Carbon 
can  combine  in  one  Molecule  is  never  more  than  Four.  One 
atom  of  carbon  is  capable  of  uniting  with  four  atoms 
of  hydrogen,  with  three  atoms  of  hydrogen  and  one  of 
chlorine,  with  two  atoms  of  hydrogen  and  two  of  chlo- 
rine, with  one  atom  of  hydrogen  and  three  of  chlorine, 
and,  finally,  with  four  chlorine  atoms.  In  short,  one 
atom  of  carbon  can  combine  with  four  atoms  of  hydro- 
gen, or  with  any  other  four  atoms  which  are  in  com- 
bining power  equivalent  to  hydrogen.  The  number 
of  single  atoms  with  which  one  atom  of  carbon  can 
combine  in  one  molecule  is  never  more  than  four. 

Valence.  Applying  what  we  have  learned  with  car- 
bon to  the  hydrogen  compounds  of  other  elements,  we 


SUBSTITUTION   OF  HYDROGEN  IN  METHANE.      179 

draw  the  following  conclusions  :  One  atom  of  hydro- 
gen combines  with  three  of  nitrogen  to  form  am- 
monia; two  atoms  of  hydrogen  combine  with  one  of 
oxygen  to  form  water;  and  one  atom  of  hydrogen 
combines  with  one  of  chlorine  to  form  hydrogen  chlo- 
ride. We  see,  then,  that  the  individual  atoms  of 
the  four  elements,  carbon,  nitrogen,  oxygen,  and  chlo- 
rine, unite  each  with  a  different  number  of  hydrogen 
atoms,  or,  to  use  another  term,  they  have  a  different 
value  toward  hydrogen.  This  we  call  a  difference  in 
valence;  and  we  say  chlorine  has  a  valence  of  one 
toward  hydrogen,  oxygen  of  two,  nitrogen  of  three, 
and  carbon  of  four. 

This  distinction  can  be  expressed  in  chemical  formu- 
lae by  writing  the  symbol  for  each  atom  in  one  mole- 
cule separately,  grouping  those  of  the  hydrogen  atoms 
round  the  atom  of  the  not-metal,  which  is  supposed  to 
join  the  different  atoms  in  the  molecule.  Thus  we 


H  H  H 

HC1          HOH       HtfH          HCH        HCH  HOC! 

H  H  Cl  Cl 

Hydrogen  chloride.    Water.          Ammonia.        Methane.  Methyl  chloride.  Methylen  chloride,  etc. 

Valence  of  Carbon,  Nitrogen,  Oxygen,  or  Chlorine  may  not 
be  the  same  toward  all  Elements.  We  must  not  suppose 
that  each  atom  of  chlorine,  oxygen,  nitrogen,  or  carbon 
can  combine  with  as  many  atoms  of  every  other  element 
as  with  those  of  hydrogen  or  of  chlorine.  That  this  is 
not  the  case  is  shown  by  the  fact  that,  so  far  as  we 
know,  one  atom  of  carbon  can  combine  with  no  more 
than  two  atoms  of  oxygen,  provided  no  other  elements 
are  present.  What  has  been  said  in  regard  to  valence, 
therefore,  must  be  confined  exclusively  to  chlorine  and 
hydrogen  compounds, 


180 


ELEMENTS   OF  CHEMISTRY. 


For  further  illustration,  the  formulae  and  composition 
of  all  the  gaseous  or  gasifiable  compounds  which  we 
have  encountered,  are  given  in  the  following  table :  — 


FORMULA. 


COMPOSITION  BY  WEIGHT. 


Hydrogen  chloride 

HC1 

One  part  of  hydrogen  to  35.5  of  chlorine. 

Water 

H20 

Two  parts  of  hydrogen  to  16  of  oxygen. 

Ammonia 

H3N 

Three  parts  of  hydrogen  to  14  of  nitrogen. 

Methane 

H4C 

Four  parts  of  hydrogen  to  12  of  carbon. 

Methyl  chloride 

H3C1C 

Three  parts  of  hydrogen  to  12  of  carbon,  35.5 
of  chlorine. 

Methylene  chloride 

H2C12C 

Two  parts  of  hydrogen  to  12  of  carbon,  71  of 

chlorine. 

Methin  chloride 

HC13C 

One  part  of  hydrogen  to  12  of  carbon,  106.5 

of  chlorine. 

Carbon  tetrachloride 

C14C 

Twelve  parts  of  carbon,  142.0  of  chlorine. 

Sulphur  dioxide 

S02 

Thirty-two  parts  of  sulphur  to  32  of  oxygen. 

Sulphur  trioxide 

S03 

Thirty-two  parts  of  sulphur  to  48  of  oxygen. 

Carbon  monoxide 

CO 

Twelve  parts  of  carbon  to  16  of  oxygen. 

Carbon  dioxide 

C02 

Twelve  parts  of  carbon  to  32  of  oxygen. 

From  this  table  it  is  apparent  that  in  one  molecule  of  carbon 
monoxide  or  carbon  dioxide  we  have  twelve  parts  of  carbon,  just 
as  we  have  in  methane  and  in  the  chlorinated  methanes.  There- 
fore, by  these  oxides  also,  the  maximum  atomic  weight  of  carbon 
is  fixed  at  twelve.  Furthermore,  we  see  that  the  least  quantity  oi 
oxygen  occurring  in  any  of  the  above  compounds  is  16,  and  that 
in  all  the  oxides  mentioned  we  have  either  16  parts  of  oxygen, 
or  some  multiple  of  16.  In  the  same  way  the  maximum  atomic 
weight  of  sulphur  is  fixed  at  32,  because  we  havo  32  parts  ot  sul- 
phur in  one  molecule  of  sulphur  dioxide  and  oi  sulphur  trioxide. 

It  has  been  demonstrated  that  the  number  of  oxygen 
atoms  with  which  one  carbon  atom  can  unite  in  either 
carbon  monoxide  or  carbon  dioxide  is  different  from  the 
number  of  hydrogen  atoms  with  which  one  carbon  atom 
can  unite  in  methane.  If  we  compare  carbon  dioxide 
and  methane,  we  see  that  two  hydrogen  atoms  have 
exactly  the  same  combining  power  as  one  oxygen  atom. 
This  difference  is  not  confined  to  the  compounds  of 


SUBSTITUTION   OF  HYDROGEN  IN  METHANE.      181 

carbon  alone.     With  all  elements  one  oxygen  atom  is 
equal  in  combining  power  to  two  hydrogen  atoms. 

The  Burning  of  Methane  is  a  Process  of  Substituting  Hy- 
drogen by  Oxygen.  The  burning  of  methane,  forming 
water  and  carbon  dioxide,  ,is  analogous  to  the  substitu- 
tion of  hydrogen  by  chlorine.  In  this  case,  however, 
two  atoms  of  oxygen  take  the  place  of  four  atoms  of 
hydrogen,  while  in  substituting  with  chlorine,  one  atom 
of  chlorine  takes  the  place  of  one  atom  of  hydrogen. 
This  comparison  is  made  more  evident  by  the  follow- 
f  ormulse :  — 

CH4     +     202      =        C02  +  2H20. 

1  mol.  of  methane  +  2  mols.  of  oxygen  =  1  mol.  of  carbon  dioxide       +  2  mol.  of  water. 

CH4     +     4C12      =        CC14          +        4HC1. 

1  mol.  of  methane     4  mols.  of  chlorine  =  1  mol.  carbon  tetrachloride     4  mols.  hydrogen  chloride. 

The  action  of  chlorine  on  hydrogen  compounds  is, 
therefore,  analogous  to  the  processes  attending  the 
combustion  of  the  same  substances  in  oxygen.  In 
the  first  case  the  chlorides  'may  be  produced,  and  in 
the  second  the  oxides.  In  either  case  heat  is  evolved 
during  the  process,  and  the  resulting  compounds  pos- 
sess less  chemical  energy  than  the  ones  used  for  the 
substitution.* 

the  Valence  of  an  Element  toward  Hydrogen  is  Constant, 
while  it  may  be  Variable  toward  Oxygen.  Finally,  the 
above  table  shows  us  that  the  number  of  oxygen  atoms 

*  In  some  cases  of  the  action  of  chlorine  or  of  oxygen  on  hydrogen 
compounds,  substitution  does  not  take  place,  but  the  not-metal  is  liber- 
ated. This  is  the  case  with  the  action  of  chlorine  or  ol  oxygen  on  ammo- 
nia. When  chlorine  reacts  wit>h  ammonia,  hydrogen  chloride  and  nitro- 
gen are  produced.  When  oxygen  reacts  with  ammonia,  water  is  formed, 
and  nitrogen  is  liberated.  The  two  processes  are  therefore  analogous. 


182  ELEMENTS   OF  CHEMISTRY. 

with  which  one  atom  of  a  given  element  can  unite  may 
vary,  while  experience  has  shown  us  that  this  is  not 
the  case  with  the  hydrogen  compounds.  The  valence  of 
an  element  toward  hydrogen  seems  to  be  constant,  while 
toivard  oxygen  it  assumes  different  values,  according  to 
circumstances.  * 

We  have  encountered  one  exception  to  the  above 
rule.  In  ammonia  one  atom  of  nitrogen  unites  with 
thre.e  atoms  of  hydrogen  in  each  •  molecule ;  but,  as  we 
have  seen  (pag^e  98),  ammonia  can  add  hydrogen  chlo- 
ride to  form  ammonium  chloride.  We  have  demon- 
strated that  in  ammonium  chloride  there  are,  one  atom 
of  nitrogen,  four  of  hydrogen,  and  one  of  chlorine  in 
each  molecule.  It  seems  possible,  therefore,  for  one 
nitrogen  atom  to  increase  the  number  of  hydrogen 
atoms  with  which  it  is  united  to  four,  provided  there 
is  some  not-metallic  element  or  group  of  elements 
(such  as  chlorine)  taken  into  the  combination  at  the 
same  time.  Toward  hydrogen  alone,  nitrogen  seems  to 
have  an  invariable  valence  of  three,  in  compounds  con- 
taining but  one  atom  of  nitrogen  in  each  molecule. 
Chemically,  it  is  said  that  ammonia  is  unsaturated  be- 
cause it  can  add  to  itself  certain  acid  compounds  in 
order  to  produce  ammonium  salts.  In  ammonium  chlo- 
ride we  have  one  atom  of  nitrogen  joined  to  four  atoms 
of  hydrogen  and  one  of  chlorine ;  the  valence  of  nitro- 
gen in  this  compound  is  consequently  five. 

Summary. 

1.  When  chlorine  acts  on  most  hydrogen  compounds 
of  the  not-metals,  hydrogen  chloride  is  produced,  and 
the  not-metal  contained  in  the  particular  compound  in 
question  is  liberated. 


SUBSTITUTION  OF  HYDROGEN  IN  METHANE.      183 

2.  If  an  excess  of  chlorine  acts  violently  on  methane 
(i.e.,    when    a  mixture    of    methane    and    chlorine    is 
ignited),    carbon    is  liberated,  and   hydrogen  chloride 
is  produced. 

3.  If  chlorine  acts  slowly  upon  methane,  substitution 
takes  place  in  such  a  way  that  one  atom  of  chlorine 
always  takes  the  place  of  one  atom  of  hydrogen.     At 
the  same  time  one  molecule  of   hydrogen    chloride  is 
formed. 

4.  The    four   hydrogen    atoms  in   one    molecule    of 
methane  can  be  successively  substituted  by  chlorine, 
producing    substances    having   the    chemical    formulse 
CH3C1,  CH2C12,  CH  C13,  and  C  C14. 

5.  The  specific  gravities  of  methane  and  of  its  sub- 
stitution products,  when  the  latter  are  heated  to  a  tem- 
perature high  enough  to  convert  them  into  gases,  confirm 
the  formulae  given  under  4. 

6.  The  atomic  weights  of  carbon  and  of  chlorine, 
determined  by  the  specific  gravities  of  gaseous  methane 
and  its  substitution  products,  are  12  and  35.5  respec- 
tively. 

7.  The  number  of  single  atoms  with  which  one  atom 
of  carbon  can  combine   in  any  one  molecule  is  never 
greater  than  4. 

8.  One  atom  of  chlorine,  oxygen,  nitrogen,  or  carbon 
can  unite  with  different  numbers  of  atoms  of  hydrogen. 
This  is  termed  a  difference  in  valence.     Chlorine  has  a 
valence  of  one  toward  hydrogen,  oxygen  of  two,  nitro- 
gen of  three,  and  carbon  of  four. 

9.  The   number  of   oxygen  atoms  with   which  one 
atom  of  these  elements  can  unite  is  different  from  the 
number  of  hydrogen  atoms.      This   difference  is  such 
that  one  oxygen  atom  can  take  the  place  of  two  hydro- 


184  ELEMENTS   OF  CHEMISTRY. 

gen  atoms,  and  is  shown  in  the  table  comparing  the 
formulse  of  the  gaseous  compounds  discussed  in  this 
work. 

10.  The  number  of  oxygen  atoms  with  which  one 
atom  of  the  above  elements  can  unite  may  vary.  This 
is  shown  by  the  existence  of  two  oxides  of  sulphur, 
sulphur  dioxide  and  sulphur  trioxide,  and  of  the  two 
oxides  of  carbon,  cabron  monoxide  and  carbon  dioxide. 


THE  FORMATION   OF  SALTS.  185 


CHAPTER   XXIII. 

THE    FORMATION    OF    SALTS    BY   DOUBLE 
DECOMPOSITION. 

Formation  of  Salts  by  Substitution  and  Neutralization. 
Thus  far  in  considering  the  formation  of  salts  we  have 
found  two  methods  available  for  the  purpose,  —  one  by 
the  action  of  metals  on  acids  (see  page  45  and  57),  the 
other  by  neutralization  of  acids  by  bases  (see  pages  48 
and  58).  In  both  cases  the  salt  is  formed  by  a  process 
of  substitution  in  which  the  metal,  either  alone  or  in 
combination  with  oxygen,  takes  the  place  of  the  hydro- 
gen in  the  acid.  The  salt  is  therefore  the  acid  in  which 
the  whole,  or  a  part,  of  the  hydrogen  has  been  replaced 
by  some  other  metal.  The  acids,  therefore,  may  be 
considered  as  salts  of  the  metal  hydrogen.  Thus,  sul- 
phuric acid  is  hydrogen  sulphate,  hydrochloric  acid  is 
hydrogen  chloride,  and  nitric  acid  is  hydrogen  nitrate ; 
while  the  salts  of  these  acids  are  termed  sulphates, 
chlorides,  and  nitrates.  The  parallelism  can  be  made 
clearer  by  comparing  the  following  formulae :  — 

H2SO4.  Na2SO4. 

Hydrogen  sulphate  (sulphuric  acid).  Sodium  sulphate. 

H  Cl.  Na  Cl. 

Hydrogen  chloride  (hydrochloric  acid).  Sodium  chloride. 

HNO3.  NaNO3. 

Hydrogen  nitrate  (nitric  acid).  Sodium  nitrate. 


186  ELEMENTS   OF  CHEMISTRY. 

Salt  Formation  by  Action  of  an  Acid  on  a  Salt.  There 
are,  however,  other  means  of  salt  formation  of  as  great 
importance  chemically  as  those  just  mentioned  which 
do  not  involve  the  action  of  an  acid  on  a  base. 

If  sodium  chloride  is  brought  in  contact  with  an  excess  of  con- 
centrated sulphuric  acid,  a  gas  passes  off,  which  from  its  proper- 
ties can  easily  be  recognized  as  hydrogen  chloride  (see  page  38 
and  Experiment  16,  Appendix).  After  the  reaction  is  completed, 
if  the  remainder  is  dissolved  in  water  and  the  solution  evapo- 
rated, crystals  of  a  salt,  which  differs  from  sodium  chloride,  will 
separate.  This  salt  does  not  liberate  hydrogen  chloride  when  sul- 
phuric acid  is  added  to  it.  It  melts  when  heated,  and  finally  gives 
off  dense  fumes  of  sulphuric  acid.  It  then  again  solidifies,  to  melt 
once  more  at  a  bright  white  heat.  In  short,  it  has  all  of  the  prop- 
erties belonging  to  primary  sodium  sulphate  (see  Experiment  34, 
Appendix).  From  sodium  chloride  and  hydrogen  sulphate  we  have 
therefore  produced  sodium  sulphate  and  hydrogen  chloride.  This 
change  can  be  made  plain  by  the  following  chemical  formulae  :  — 

Na  Cl  +  HHSO4  =  H  Cl  +  Na  HSO4 . 

A  reaction  of  this  kind  is  termed  a  double  decompo- 
sition, since  both  the  sulphuric  acid  and  the  sodium 
chloride  have  been  altered  in  such  a  way  that  sodium 
and  hydrogen  have  exchanged  places.  Hydrogen  chlo- 
ride is  a  gas,  and,  as  a  consequence,  passes  off,  so  that 
at  the  end  of  the  experiment  nothing  remains  but  pri- 
mary sodium  sulphate,  together  with  the  excess  of  sul- 
phuric acid  which  has  been  used.  In  such  a  reaction 
the  action  of  sodium  chloride  is  analogous  to  that  of 
sodium  hydroxide  on  sulphuric  acid ;  in  one  case  so- 
dium chloride  and  sulphuric  acid  produce  sodium  sul- 
phate and  hydrogen  chloride ;  in  the  other,  sodium 
hydroxide  and  sulphuric  acid  form  sodium  sulphate 
and  hydrogen  oxide  (water).  It  follows  from  this  that 
the  neutralization  of  an  acid  by  a  base  is  also  a  reaction 
involving  a  double  decomposition. 


THE  FORMATION  OF  SALTS.  187 

Double  Decompositions  between  Two  Salts.  The  reactions 
which  have  been  cited  involve  the  action  of  a  salt  or  a 
base  on  an  acid.  We  can,  however,  »have  other  double 
decompositions,  in  which  two  salts  change  each  other 
so  as  to  produce  two  new  salts,  in  which  case  the 
metals  exchange  places.  If,  for  example,  a  solution 
of  barium  chloride  is  brought  in  contact  with  one  of 
sodium  sulphate,  a  double  decomposition  takes  place, 
while  the  insoluble  barium  sulphate  is  separated.  This 
change  can  be  expressed  as  follows :  — 

Barium  chloride+  Sodium  sulphate  =  Barium  sulphate  +  Sodium  chloride. 

soluble  soluble  insoluble  soluble. 

The  separation  of  an  insoluble  substance  from  a  solu- 
tion by  double  decomposition  is  termed  precipitation. 
Processes  similar  to  the  above  are  of  such  frequent 
occurrence  in  chemical  work  as  to  warrant  the  estab- 
lishment of  the  following  arbitrary  rule: — 75 

Double  decompositions  occur  whenever  a  volatile  or  an 
insoluble  substance  can  be  produced. 

EXAMPLES:  — 

1.  Calcium  chloride  +  Potassium  carbonate  =  Calcium  carbonate  +  Potassium  chloride. 

soluble  soluble  insoluble  soluble. 

2.  Barium  chloride  +  Sodium  carbonate=  Barium  carbonate  +  Sodium  chloride. 

soluble  soluble  insoluble  soluble. 

3.  Sodium  chloride  4-  Silver  nitrate  =  Silver  chloride  +  Sodium  nitrate. 

soluble        soluble        insoluble         soluble. 

4.  Magnesium  sulphate  +  Barium  chloride  =  Barium  sulphate  +  Magnesium  chloride. 

soluble  soluble          insoluble  soluble. 

In  the  above  changes,  the  result  is  such  that  two 
soluble  salts  so  react  that  they  completely  decompose 
each  other  in  order  to  produce  two  new  salts,  one  of 
which  is  insoluble  in  the  medium  in  which  the  re- 


188  ELEMENTS   OF  CHEMISTRY. 

action  takes  place.  Of  course,  if  any  substance  is  added 
to  the  solvent  which  will  prevent  the  formation  of 
an  insoluble  substance,  then  precipitation  cannot  take 
place.  For  example,  the  carbonates  are  decomposed 
by  acids,  with  the  liberation  of  carbon  dioxide  and 
water.  It  follows  that  reactions  1  and  2  cannot  take 
place  if  an  acid  be  present,  as  the  carbonate  of  calcium 
which  should  be  formed  would  be  decomposed  by  this 
acid.  If,  however,  in  reaction  2  the  acid  were  sulphuric 
acid,  then  a  precipitation  of  the  insoluble  barium  sul- 
phate would  take  place,  instead  of  that  of  the  equally 
insoluble  barium  carbonate.76 

Causes  of  Double  Decomposition.  Electrolysis.  The  rea- 
son why  such  double  decompositions  take  place  is  prob- 
ably to  be  found  in  the  following  explanation :  - 

If  the  two  poles  of  a  battery  are  placed  in  a  salt  solution,  the 
salt  will  be  decomposed  by  the  electric  current  which  is  conducted 
from  one  pole  to  the  other.  Of  these  two  poles,  one  is  positive 
and  the  other  negative.  The  current  passes  from  the  negative  to 
the  positive  pole.  Substances  which,  like  salts,  are  decomposed 
by  an  electric  current  are  termed  electrolytes.  The  terminals 
from  which  the  current  enters  or  leaves  the  solution  are  called 
the  electrodes.  The  positive  electrode  is  the  anode,  and  the  nega- 
tive one  the  kathode.  The  portions  into  which  the  electrolyte 
separates  are  termed  the  ions.  The  ion  which  passes  off  at  the 
positive  pole  (itself  negative)  is  the  anion,  that  passing  off  at  the 
negative  pole  (itself  positive)  is  termed  the  kation.  For  example, 
hydrochloric  acid  is  separated  by  means  of  an  electric  current  into 
its  ions,  hydrogen  and  chlorine.  The  kation  is  hydrogen,  the 
anion  is  chlorine ;  and,  if  proper  means  are  taken  to  collect  the 
gases,  pure  hydrogen  can  be  obtained  from  the  negative  pole  and 
chlorine  from  the  positive,  as  was  done  in  the  experiments  with 
hydrochloric  acid  in  Experiment  19,  Appendix.  In  the  same  way 
a  solution  of  sodium  chloride  is  separated  into  sodium  (the  ka- 
tion) and  chlorine  (the  anion).  A  solution  of  potassium  chloride 


THE  FOEMATION  OF  SALTS.  189 

will  separate  into  potassium  (the  kation)  and  chlorine  (the  anion), 
or  a  solution  of  potassium  sulphate  (chemical  formula  K0  SO4)  into 
potassium  (kation)  and  the  group  SO4  (anion).*  Only  such  solu- 
tions as  contain  substances  capable  of  separation  into  their  ions 
have  the  power  of  conducting  electricity.  Hence  it  seems  proba- 
ble that  salts  'separate,  at  least  partially,  when  they  are  dissolved, 
even  if  no  electric  current  is  passed  through  them.  This  supposi- 
tion is  borne  out  by  a  number  of  other  experimental  facts  of  too 
complex  an  order  to  be  mentioned  here. 

A  solution  of  sodium  chloride  contains  the  ions  rep- 
resented by  the  symbols  Na  and  Cl,  one  of  potassium 
chloride,  K  and  Cl,  one  of  potassium  sulphate,  2  K  and 
SO4,  and  so  on.  We  cannot,  however,  demonstrate  the 
presence  of  the  uncombined  ions  in  such  a  solution 
(i.e.,  we  cannot  prove  the  presence  of  free  chlorine  and 
free  sodium  in  a  solution  of  sodium  chloride)  so  long 
as  these  elements  are  not  collected  at  electrodes  by 
the  action  of  an  electric  current. 

It  can  be  supposed,  for  example,  that,  when  sodium  chloride 
separates  into  Na  and  Cl,  the  individual  atoms  do  not  remain 
permanently  isolated,  but  that  they  frequently  recombine.  Each 
atom  of  chlorine,  however,  does  not  unite  with  the  same  atom  of 
sodium  with  which  it  was  originally  joined,  but  with  another, 
and  again  separates  and  rejoins  others  in  the  throng  of  atoms 
which  it  may  encounter. 

Change  in  the  Conditions  if  an  Insoluble  Substance  can  be 
formed.  According  to  this  theory,  if  a  solution  of  sodium 
chloride  is  mixed  with  one  of  potassium  sulphate,  we 
shall  have  present  the  ions  of  Na  -j-  Cl  and  2  K  -f  SO4. 
Such  a  mixture  is  obviously  practically  identical  with 
one  of  potassium  chloride  and  sodium  sulphate,  for  the 

*  Of  course,  the  potassium  or  sodium,  being  in  the  presence  of  water, 
will  react  again  with  that  liquid.  The  metals  themselves  can  only  be 
separated  by  electrolyzing  the  fused  salts,  when  the  water  is  present. 


190  ELEMENTS   OF  CHEMISTRY. 

latter  contains  ions  K  +  Cl  and  2  Na  +  SO4.  The  result 
would  then  be  the  same  as  if  on  mixing  potassium  chlo- 
ride with  sodium  sulphate  we  were  to  have  partial 
double  decomposition  forming  sodium  chloride  and  po- 
tassium sulphate,  both  of  which  are  soluble  in  water. 
An  entirely  different  effect  is  obtained  if  one  of  the 
salts  produced  is  insoluble.  For  example,  silver  nitrate 
in  solution  with  sodium  chloride  undergoes  double  de- 
composition, forming  the  insoluble  silver  chloride  and 
the  soluble  sodium  nitrate.  Now,  in  a  solution  of  silver 
nitrate  we  have  the  ions  Ag*  and  NO3  (the  chemical 
formula  of  silver  nitrate  is  Ag  NO3),  and  in  a  solution 
of  sodium  chloride  we  have  the  ions  Na  and  Cl.  The 
chemical  structure  of  such  a  solution  could  be  repre- 
sented by  the  formula  — 

Na  +  Cl  +  Ag  +  N03. 

kation      anion     kation        anion. 

The  kation  Ag  is  capable  of  uniting  with  the  anion 
Cl,  when  it  comes  in  contact  with  it,  and  the  resulting 
compound  (Ag  Cl,  silver  chloride)  is  insoluble.  It  is, 
therefore,  precipitated,  and  separates  from  the  solution. 
A  second  kation  Ag  can  come  in  contact  with  a  second 
anion  Gl,  and  so  on  until  all  of  the  silver  and  chlorine 
present  are  separated  as  silver  chloride.  The  solution 
will  then  contain  only  the  ions  Na  and  NO3t,  which, 
after  the  solvent  is  evaporated,  will  leave  sodium  ni- 
trate. What  is  true  of  the  above  reaction  must  be 
true  in  every  case  where  salts  in  solution  are  brought 

*  The  chemical  symbol  for  one  atom  of  silver  is  Ag,  from  the  latin  ar- 
gentum  (silver). 

t  Of  course  if  more  sodium  chloride  than  is  necessary  to  form  silver 
chloride  with  all  of  the  silver  in  solution  is  present,  then  that  excess 
remains  after  the  double  decomposition,  and  vice  versa. 


THE  FORMATION  OF  SALTS.  191 

in  contact,  when  one  of  the  products  of  the  union  of  the 
ions  is  insoluble.  If  one  of  the  constituents  is  volatile, 
it  is  just  as  surely  removed  from  the  solution  as  if  it 
were  insoluble.  From  the  above  considerations  it  fol- 
lows that  complete  double  decomposition  must  take 
place  whenever  insoluble  or  a  volatile  substance  can 
be  produced. 

Electrolysis  of  Water  and  of  Hydrochloric  Acid.     The 

process  of  electrolysis  has  been  repeatedly  used  during 
the  progress  of  this  work.  Thus  water  acidulated  with 
sulphuric  acid  was  decomposed  into  hydrogen  and  oxy- 
gen by  the  electric  current  (see  page  21).  Pure  water 
is  not  a  conductor  of  electricity,  and  consequently  is 
not  subject  'to  electrolysis.  But  when  sulphuric  acid 
is  dissolved  in  water  the  mixture  becomes  a  conductor, 
and  if  an  electric  current  is  passed  through  it,  the 
kation  H2  separates  at  the  negative  pole,  and  the  anion 
SO4  at  the  positive.  But  SO4  is  not  capable  of  exist- 
ence as  such ;  it  breaks  down  into  sulphur  trioxide 
(SO8,  see  page  56)  and  oxygen,  which  passes  off.  The 
sulphur  trioxide,  being  the  anhydride  of  sulphuric  acid, 
dissolves  in  water  to  form  sulphuric  acid,  so  that  no 
loss  of  the  latter  substance  takes  place.  The  only 
compound  which  is  decomposed  is  therefore  water. 

This   change    may   be    represented    as   follows   by   chemical 
symbols  :  — 

H2  SO4      =  H.2    +  SO4 . 

Sulphuric  acid  =  kation  +  anion. 

SO4     =  SO3  +      O. 

The  anion  =  sulphur  trioxide  +  oxygen. 
S03          +H20  =     H2S04. 

Sulphur  trioxide  +    water  =  sulphuric  acid. 

The  substances  passing  off  are  hydrogen  and  oxygen. 


192  ELEMENTS   OF  CHEMISTRY. 

A  concentrated  solution  of  hydrochloric  acid  is  de- 
composed into  hydrogen  and  chlorine  by  the  electric 
current  (see  page  40).  In  this  case  the  kations  of  hy- 
drogen separate  at  the  negative  pole  and  the  anions  of 
chlorine  at  the  positive. 

Neutralization  of  Bases  by  Acids.  To  illustrate  the 
neutralization  of  bases  by  acids,  let  us  take  the  neutral- 
ization of  hydrochloric  acid  by  sodium  hydroxide.  This 
change  can  be  represented  by  the  chemical  formulae  — 

HC1        +     NaOH      =      NaCl       +  HOH. 

Hydrochloric  acid  +  Sodium  hydroxide  =  Sodium  chloride     +     Water. 

In  solution,  hydrochloric  acid  exists  as  the  ions  H  -f  Cl, 
and  sodium  hydroxide  as  the  ions  Na  +«OH.     When 
these  are  brought  in  contact  the  ions  would  be  I'- 
ll +  Cl  +  Na  +  OH. 

Now,  the  only  substance  which  is  present  in  excess,  and 
which,  while  being  capable  of  formation  from  the  above 
constituents,  would  not  have  a  tendency  toward  ioniza- 
tion,  is  water.  Water,  therefore,  would  be  produced  by 
the  interaction  of  these  ions,  while  the  ions  Na  -f-  Cl 
alone  would  be  left.  The  same  result  is  obtained  when 
other  acids  and  bases  are  brought  in  contact;  so  that 
one  of  the  chief  reasons  for  the  fact  that  acids  and  bases 
neutralize  each  other  is  found  in  the  formation  of  water. 
Of  course  the  neutralization  would  be  the  more  rapid 
and  complete  the  more  readily  ionization  took  place  on 
solution. 

The  process  of  electrolysis  has  been  a  most  impor- 
tant one  in  the  history  of  chemistry.  By  means  of  an 
electric  current,  Davy  first  succeeded  in  decomposing 


THE  FORMATION   OF  SALTS.  193 

caustic  potash  (potassium  hydroxide)  and  caustic  soda 
(sodium  hydroxide),  and  in  isolating  the  metals  potas- 
sium and  sodium.  Before  that  time  caustic  potash  and 
caustic  soda  were  considered  elements. 

Summary. 

1.  Acids  are  salts  of  the  metal  hydrogen,  and  salts 
are  acids  in  which  the  hydrogen  has  been  replaced  by 
other  metals. 

2.  Salts  of  some  acids  can  be  formed  by  the  action  of 
those  acids  upon  the  salt  of  some  other  acid ;  for  exam- 
ple, by  the  action  of  sulphuric  acid  on  sodium  chloride 
we  can  produce  sodium  sulphate. 

3.  Such  reactions  are  termed  double  decompositions, 
for  in  them  the  metal  of  the  salt  and  the  hydrogen  of 
the  acid  acting  upon  it  exchange  places. 

4.  The  neutralization  of  a  base  by  an  acid  is  also  a 
double  composition. 

5.  Double  decomposition  can  also  take  place  between 
two  salts.     In  such  a  case  the  metals  in  the  two  salts 
exchange    places.       Complete    double    decompositions 
occur  if  a  volatile  or  an  insoluble  substance  is  formed 
during  the  reaction.     • 

6.  Salt  solutions  are  decomposed  (electrolyzed)  by 
the  electric  current.     The  salt  separates  into  two  ions, 

—  the  kation  (metallic  constituent)  and  the  anion  (not- 
metallic  constituent).  Only  such  solutions  as  contain 
substances  separable  by  electrolysis  conduct  electricity. 

7.  Salts,  when  dissolved,  separate    into    their  ions, 
at  least  in  part.     The  presence  of  these  ions  cannot 
be  demonstrated  by  ordinary  means.     They  can,  how- 
ever, be  collected  at  the  electrodes  by  the  action  of  the 
electric  current. 


194  ELEMENTS   OF  CHEMISTRY. 

8.  When,  on  mixing  two  salts,  a  new  insoluble  salt 
can  be  produced,   then  a  precipitate   of   such  salt  is 
formed.      The  remaining  two  ions  stay  in  the  solution 
and  form  the  second  new  salt  on  evaporation  of  the 
solvent.     The  case  is  the  same  if  one  of  the  substances 
produced  is  volatile. 

9.  In  electrolyzing  water  acidulated  with  sulphuric 
acid,  the  acid  is  decomposed  into  its  ions,  hydrogen  and 
a  group  of  elements  represented  by  the  formula  SO4 . 
The  latter  separates  at  the  positive  pole,  and  breaks 
down  into  sulphur  trioxide  (SO3)  and  oxygen.     The 
elements  which  pass  off  are,  therefore,  hydrogen  and 
oxygen.     The  sulphur  trioxide  remains,  and,  with  the 
water  which  is  present,  regenerates  sulphuric  acid. 

10.  The  process   of  neutralization  is   explained  by 
the  decomposition  of  the  acid  and  the  base  into  their 
ions.     Two  of  these  ions  must  always  be  hydrogen  and 
hydroxyl  (H  and  OH),  and  these  unite  to  form  water. 
There  would  then  remain  in  solution  only  the  metallic 
and  notnnetallic  ions  which  were  originally  present  as 
constituents  of  the  base  and  acid  respectively.     These 
ions,  when  the  solvent  is  evaporated,  unite  to  form  the 
salt.  * 


CHEMICAL  NATUEE  OF  OTHER   ELEMENTS.       195 


CHAPTER   XXIV. 

THE  CHEMICAL  NATURE  OF  SOME  OTHER  ELE- 
MENTS AND  COMPOUNDS  RELATED  TO  THOSE 
WHICH  HAVE  BEEN  STUDIED. 

Chemical  Elements  are  Separable  into  Groups  and  Fami- 
lies. The  chemical  elements  are  not  individuals  each 
with  distinct  characteristics  which  do  not  recur  in  the 
natural  history  of  the  others.  They  are  members  of 
certain  groups  or  families,  the  representatives  of  which 
are  all  more  or  less  related  to  each  other,  both  chemi- 
cally and  physically.  To  trace  out  these  relations  in 
their  entirety  would  involve  too  great  extension  of  the 
limits  of  an  elementary  work.  We  can  call  attention 
only  to  a  few  individuals  which  are  closely  related  to 
the  elements  which  we  have  studied. 

Elements  of  the  Chlorine  Family.  Chlorine  is  very 
closely  connected,  chemically,  with  three  other  elements, 
— fluorine,  bromine,  and  iodine.  These  substances,  like 
chlorine,  are  always  found  in  nature  in  combination 
with  metals,  as  fluorides,  bromides,  and  iodides.  The 
bromides  and  iodides  of  potassium  and  sodium  are 
generally  found  in  conjunction  with  the  chlorides  of 
the  same  metals,  but  they  are  present  in  lesser  quantity 
on  the  earth's  surface.  In  sea-water  there  are  large 
amounts  of  sodium  chloride  and  small  amounts  of 
sodium  bromide  and  iodide.  All  the  elements  of  the 


196 


ELEMENTS   OF  CHEMISTRY. 


chlorine  family,  with  the  exception  of  fluorine,  can  be 
isolated  from  their  salts  by  the  same  means. 

Of  these  four  elements,  fluorine  has  the  smallest 
atomic  weight,  chlorine  the  next  higher,  bromine  the 
next,  and  iodine  the  greatest.  In  the  following  table 
these  elements  are  given  in  the  order  of  their  increasing 
atomic  weights,  while  the  physical  properties,  which 
vary  regularly  in  the  order  given,  are  placed  opposite 
each  individual :  — 


03    • 

h 

— 

U  H 

'-'  ^  W 

O  pJ 

O  oj 

gw 

^   U3   Q 

Sg 

O  -1 

§s" 

USUAL  CONDITION. 

§2 

35 

pS 

5ao 

H  « 

^ 

iJ  ^ 

0  ° 

^0 

a  ^02 

*5" 

0 

»* 

^oS 

Fluorine 

19. 

1.364 

Slightly  yellow  gas 

Yellow 

— 





Chlorine 

35.5 

2.46 

Yellowish-green  gas 

Yellow 

—  35° 

—  102° 

Bromine 

80. 

5.54 

Dark-brown  liquid 

Brown 

63° 

—     7°.3 

Iodine 

127.6 

8.84 

Crystalline  black  solid 

Violet 

200° 

114° 

4.94 

As  is  seen  from  the  above,  the  specific  gravities,  both 
of  the  gaseous  and  solid  substances,  increase  with  in- 
creasing atomic  weight,  the  color  deepens,  and  finally 
(with  iodine)  becomes  black.  The  boiling  and  melting 
points  also  increase  with  increasing  atomic  weight. 

Elements  of  the  Oxygen  Family.  Oxygen  and  sulphur 
also  belong  to  a  family  which  contains  four  elements. 
In  order  to  show  the  similarity  to  the  chlorine  family 
in  the  changes  brought  about  by  the  increase  in  atomic 
weight,  a  table  containing  the  principal  physical  proper- 
ties of  these  elements  is  given  on  opposite  page. 


Elements  of  the  Nitrogen  Family.      In    the   family  of 
which  nitrogen  is  a  member,  we  have  five  individuals, 


CHEMICAL  NATURE  OF  OTHER   ELEMENTS.       197 


O   tx   CH 

„ 

&  J! 

°wn 

W  0 

g| 

ff 

USUAL  CONDITION. 

tf  o 
0  % 

3  g 
o  ® 

ELTIX 
JOINT. 

&S3 
w^« 

coOg 

0 

w" 

^ 

UJoS 

Oxygen 

16. 

1.105 

Colorless  gas 

Colorless 

—  182° 





Sulphur 

32. 

2.2 

Yellow  solid 

Brown 

440° 

114° 

2.045 

Selenium 

78. 

5.7 

Dark-brown,         almost 

Brown 

665° 

217° 

4.5 

black    solid 

Tellurium 

125. 

9. 

Metallic  appearing  solid 

Orange 

500° 

6.25 

—  nitrogen,  phosphorus,  arsenic,  antimony,  and  bis- 
muth. Of  these,  the  element  with  the  smallest  atomic 
weight  (nitrogen)  is  completely  a  not-metal,  while  that 
with  the  highest  (bismuth)  is  a  metal,  physically  and 
chemically.  In  this  family,  therefore,  we  have  the  same 
change  in  properties,  with  increasing  atomic  weight,  as 
was  observed  in  the  families  of  which  chlorine  and  oxy 
gen  are  representatives.  This  fact  will  be  plainer  by 
consulting  the  table  :  — 


TOMIC 
EIGHT. 

ECIFIC 
AVITT 

GASES. 

USUAL  CON- 
DITION. 

to 

°« 

O  co 

S5 

O    • 

2  ^ 

H  ^ 

iff 

w  ^W 

*t 

&G% 

^ 

& 

s<? 

02O  ta 
O 

Nitrogen 

14 

.972 

Colorless  gas 

Colorless 

-193 

-203" 

— 

Phosphorus 

31 

4.16 

Yellow  solid 

Colorless 

290° 

440 

1.83 

Arsenic 

75 

10.3 

Steel-gray  solid 

Lemon 

450°* 



5.76 

yellow 

Antimony 

120 

9.78  1 

Silver  white  solid 



About  1200° 

425° 

6.7 

Bismuth 

208.9 

10.1 

Reddish  metallic 



1400°  (?) 

270° 

9.93 

solid 

*  Arsenic  vaporizes  without  previously  melting. 

t  The  specific  gravity  of  antimony  vapor  is  less  than  that  of  arsenic. 
This  is  because  arsenic,  when  a  gas,  has  molecules  formed  of  four  atoms, 
while  antimony,  as  a  gas,  has  molecules  formed  of  two  or  less.  The 
molecules  of  gaseous  bismuth  consist,  in  part,  of  but  one  atom,  hence  its 
low  specific  gravity. 


198  ELEMENTS   OF  CHEMISTRY. 

In  all  these  families  which  have  been  mentioned,  the 
increase  in  atomic  weight,  as  we  pass  from  member  to 
member,  brings  with  it  an  increase  in  specific  gravity 
both  as  a  vapor  and  as  a  solid.  There  is  also  a  gradual 
change  from  a  not-metallic  to  a  metallic  element,  or, 
at  least  in  the  chlorine  family,  to  an  element  which 
is  more  like  a  metal  than  the  original  member. 

Comparison  of  the  Three  Families.  As  a  rule  then,  in 
these  three  families,  the  specific  gravities  of  the  ele- 
ments, both  when  taken  as  gases  and  as  solids,  increase 
as  the  atomic  weight  increases,  and  at  the  same  time 
the  melting-points  become  higher.  The  elements  with 
the  lowest  atomic  weights  are  not  metallic,  while  those 
with  the  highest  are  either  metallic  in  appearance  (tel- 
lurium and  arsenic,  antimony  and  bismuth),  or  at  least 
approach  the  metallic  character  (iodine).  In  chemical 
character  we  find  the  same  close  family  relationship. 

Chemical  Resemblances  in  the  Hydrogen  Compounds. 
Our  attention,  in  the  preceding  portions  of  this  work, 
has  mainly  been  directed  to  a  consideration  of  com- 
pounds of  the  elements  with  hydrogen.  Therefore,  in 
calling  attention  to  the  chemical  resemblances  of  the 
members  of  the  three  families  under  discussion,  we 
shall  use  the  hydrogen  compounds  as  a  basis. 

Hydrogen  Compounds  of  the  Chlorine  Family.  Fluorine, 
chlorine,  bromine,  and  iodine  are  capable  of  producing 
one  hydrogen  compound  each ;  and  this,  like  hydrogen 
chloride,  is  a  gas  at  ordinary  temperatures.*  These 
hydrogen  compounds  are  all  readily  soluble  in  water, 

*  Hydrogen  fluoride  boils  at  19°,  and  is,  therefore,  a  gas  at  summer 
heat,  but  a  liquid  at  winter  temperature. 


CHEMICAL  NATURE  OF  OTHER   ELEMENTS.       199 

and  their  solutions  are  acids,  capable  of  neutralizing 
bases  to  form  salts.  These  substances  are  termed  hy- 
drofluoric, hydrochloric,  hydrobromic,  and  hydroiodic 
acids.  The  salts  derived  from  the  acids  by  replacing 
the  hydrogen  by  other  metals  are  the  fluorides,  chlo- 
rides, bromides,  and  iodides.  These  hydrogen  com- 
pounds are  all  formed  on  the  same  structural  plan ;  i.e., 
by  the  union  of  equal  volumes  of  hydrogen  and  of  the 
not-metallic  element  (fluorine,  chlorine,  bromine,  or 
iodine),  so  that  their  smallest  particles  contain  one 
atom  of  hydrogen  and  one  atom  of  fluorine,*  chlorine, 
bromine,  or  iodine.  The  chemical  formulae  of  these 
substances  are,  therefore  — 

HF,  the  chemical  symbol  for  one  atom  of  fluorine  being  F. 
H  Cl,  the  chemical  symbol  for  one  atom  of  chlorine  being  Cl. 
H  Br,  the  chemical  symbol  for  one  atom  of  bromine  being  Br. 
HI,  the  chemical  symbol  for  one  atom  of  iodine  being  I. 

The  stability  of  these  hydrogen  compounds  diminishes 
as  the  atomic  weight  of  the  not-metallic  element  in- 
creases. As  a  consequence,  hydrogen  iodide  is  much 
more  readily  decomposed  than  hydrogen  bromide,  and 
hydrogen  bromide  more  readily  than  hydrogen  chloride. 
Hydrogen  fluoride  has  not  been  separated  into  its  ele- 
ments by  heat  alone.  Hydrogen  chloride  is  decom- 
posed only  at  a  high  white  heat,  while  hydrogen  iodide 
can  be  broken  down  by  a  red-hot  wire  placed  in  the  gas. 
The  relative  stability  of  the  last  three  of  these  compounds 
is  readily  shown  by  the  following  experiments :  - 

If  a  few  drops  of  a  solution  of  chlorine  in  water  are  added  to  a 
solution  of  hydriodic  acid,  iodine  will  at  once  separate  and  hydro- 

*  The  specific  gravity  of  hydrogen  fluoride,  as  a  gas,  shows  that  this 
suhstance  has  a  molecule  composed  of  two  atoms  of  hydrogen  and  two  of 
fluorine.  Its  formula,  therefore,  heing  H2  F2. 


200  ELEMENTS   OF  CHEMISTRY. 

chloric  acid  be  formed.  Chlorine,  therefore,  expells  iodine  from 
its  hydrogen  compound,  to  form  the  more  stable  hydrochloric 
acid.  In  the  same  way  bromine  is  replaced  by  chlorine,  when 
the  latter  element  is  brought  in  contact  with  hydrobromic  acid ; 
and  lastly,  iodine  is  expelled  from  hydroiodic  acid  by  bromine.77 

Hydrogen  Compounds  of  Elements  of  the  Oxygen  Family. 
The  elements  of  the  family  of  which  oxygen  is  a  mem- 
ber all  form  hydrogen  compounds  which,  with  the  ex- 
ception of  hydrogen  oxide  (water),  are  colorless  gases 
at  ordinary  temperatures.  These  hydrogen  compounds 
are  all  of  the  same  structural  plan,  for  their  molecules 
are  formed  of  two  atoms  of  hydrogen  and  one  atom  of 
the  not^metallic  element.  This  will  be  seen  from  the 
following  chemical  formulae  :  — 

H2  O,  water. 

H2  S,  hydrogen  sulphide. 

H2  Se,  hydrogen  selenide  (the  chemical  symbol  for  one  atom 

of  selenium  is  Se). 
H2  Te,  hydrogen  telluride  (the  chemical  symbol  for  one  atom 

of  tellurium  is  Te). 

In  regard  to  their  relative  stability,  these  hydrogen 
compounds  follow  the  same  rule  as  in  the  case  of 
chlorine,  bromine,  and  iodine ;  the  higher  the  atomic 
weight  of  the  element  forming  them  is,  the  more  easily 
are  they  decomposed.  Thus,  water  is  broken  down 
into  hydrogen  and  oxygen  only  at  a  high  white  heat, 
while  hydrogen  telluride  is  so  unstable  that  it  decom- 
poses in  part,  even  at  ordinary  temperatures.  The 
compounds  hydrogen  sulphide  and  hydrogen  selenide 
lie  between  these  two  extremes. 

Hydrogen  Sulphide,  Preparation  and  Properties.  Next 
to  water,  the  most  important  hydrogen  compound  of 


CHEMICAL   NATURE   OF  OTHER   ELEMENTS.       201 

the  elements  of  the  oxygen  family  is  hydrogen  sulphide. 
This  substance  is  so  frequently  used  as  a  laboratory 
reagent  that  a  brief  description  of  its  properties  and 
its  reactions  is  necessary. 

The  preparation  of  hydrogen  sulphide  involves  the 
same  principle  as  that  of  hydrogen  chloride.  The  sul- 
phide of  a  metal  is  treated  with  an  acid,  just  as  sodium 
chloride  is  brought  in  contact  with  sulphuric  acid,  in 
order  to  liberate  hydrogen  chloride ;  for  example  :  - 

Sulphide  of  iron  (ferrous  sulphide)  with  hydrochloric  acid 
forms  chloride  of  iron  (ferrous  chloride)  and  hydrogen  sulphide. 

Sulphide  of  zinc  with  sulphuric  acid  forms  zinc  sulphate  and 
hydrogen  sulphide. 

All  metallic  sulphides,  however,  are  not  decomposed 
by  acids,  there  being  a  considerable  number  which  are 
not  acted  upon.  In  the  laboratory  preparation  of  hy- 
drogen sulphide,  it  is  advisable  to  decompose  ferrous 
sulphide  with  dilute  sulphuric  acid,  producing  ferrous 
sulphate  and  hydrogen  sulphide.78  In  chemical  nota- 
tion this  reaction  can  be  expressed  as  follows :  - 

FeS        +    H2SO4    =    FeSO4     +         H2S. 

Ferrous  sulphide  +  Sulphuric  acid  =  Ferrous  sulphate  +  Hydrogen  sulphide. 

This  reaction,  therefore,  involves  a  double  decomposition,  and 
is  entirely  analogous  to  the  neutralization  of  a  base  by  an  acid,  as 
the  following  reaction  will  demonstrate  :  — 

FeO          +    H2S04    =    FeS04     +H2O. 

Ferrous  oxide  (a  base)  +  Sulphuric  acid  =  Ferrous  sulphate  +    Water. 

Properties  of  Hydrogen  Sulphide.  Under  ordinary  conditions, 
hydrogen  sulphide  is  a  gas  with  a  most  disagreeable  odor.  When 
inhaled,  even  in  comparatively  small  quantities,  it  is  poisonous. 
It  is  soluble  in  water  in  considerable  quantity  (one  cubic  centi- 
metre of  water  dissolves  three  of  hydrogen  sulphide  at  18°) ;  and 
its  solution,  when  allowed  to  stand  exposed  to  the  air,  gradually 


202  ELEMENTS   OF  CHEMISTRY. 

deposits  sulphur,  owing  to  the  fact   that  it  is   oxidized.       This 
change  can  chemically  be  repeated  as  follows  :  — 

H2S          +    O    ==  H20  +     S. 

Hydrogen  sulphide  +  Oxygen  =    Water     +  Sulphur. 

It  naturally  follows  from  the  above  that  hydrogen  sulphide 
burns  in  the  air  just  as  does  methane.  When  methane  burns,  it 
forms  carbon  dioxide  and  water ;  when  hydrogen  sulphide  burns 
in  an  excess  of  oxygen,  it  forms  sulphur  dioxide  and  water. 

Formation  of  Insoluble  Sulphides  by  Double  Decomposi- 
tion between  Hydrogen  Sulphide  and  the  Salts  of  Metals. 
Most  sulphides  of  the  metals  are  not  soluble  in  water ; 
and,  as  has  been  mentioned  above,  a  considerable  num- 
ber are  not  decomposed  by  dilute  acids.  Consequently, 
in  many  cases,  the  insoluble  sulphides  are  precipitated 
from  solutions  of  metallic  salts  by  the  addition  of  hy- 
drogen sulphide.79  For  example  :— 

Copper  sulphate  4-  Hydrogen  Sulphide  =  Copper  sulphide  -*-  Sulphuric  acid. 

Soluble  soluble  insoluble         soluble. 

Lead  acetate  -(-Hydrogen  sulphide  =  Lead  sulphide  +  Acetic  acid. 

Soluble  soluble          insoluble       soluble. 

Some  Sulphides  Insoluble  in  Water  are  Soluble  in  Dilute 
Acids.  The  sulphides  of  certain  metals,  although  they 
are  insoluble  in  water,  are  decomposed  by  dilute  acids, 
and  hence  are  soluble  in  the  latter.  This  is  the  case 
with  ferrous  sulphide  or  zinc  sulphide  which  were  men- 
tioned above.  Under  these  circumstances,  it  is  obvious 
that  no  precipitate,  or  at  least  very  little  precipitate,  of 
the  sulphide  is  produced  by  hydrogen  sulphide ;  for, 
as  the  action  of  hydrogen  sulphide  in  producing  the 
sulphide  of  the  metal  liberates  an  acid,  it  follows  that 
the  latter  would  reverse  the  reaction  as  soon  as  it  is 
formed,  In  other  words,  it  would  attack  the  sulphide, 


CHEMICAL   NATURE   OF  OTHER   ELEMENTS.       203 

and  reproduce  the  original  salt  of  the  metal  together 
with  hydrogen  sulphide.     For  example  :  — 

Zinc  sulphate  +  Hydrogen  sulphide  =  Zinc  sulphide  +  Sulphuric  acid. 


Soluble  soluble          insoluble         soluble. 

After  a  certain  quantity  of  sulphuric  acid  has  been 
formed,  the  latter  attacks  the  zinc  sulphide  in  order  to 
reproduce  zinc  sulphate  and  hydrogen  sulphide.  If  care 
is  taken  to  neutralize  the  acid  as  fast  as  it  is  formed, 
the  precipitation  is  complete.  The  neutralization  can 
be  accomplished  by  adding  the  sulphide  of  an  alkali 
metal  instead  of  hydrogen  sulphide,  thus  :  — 

Zinc  sulphate  +  Potassium  sulphide  =  Zinc  sulphide  -f  Potassium  sulphate. 

Soluble  soluble  insoluble  soluble. 

In  this  case  no  free  sulphuric  acid  is  formed,  and 
hence  no  solution  of  the  zinc  sulphide  takes  place.80 
The  chemical  importance  of  hydrogen  sulphide  is 
mainly  found  in  its  use  as  a  means  of  separating  cer- 
tain groups  of  metals  from  each  other  when  they  are 
found  in  solution  as  salts.  If  hydrogen  sulphide  is 
added  to  the  acid  solution  of  the  salts  of  a  number 
of  metals,  some  of  which  form  sulphides  insoluble  in 
dilute  acids,  while  others  produce  soluble  sulphides, 
it  is  obvious  that  the  metals  of  the  first  class  can  be 
completely  separated  by  the  addition  of  the  hydrogen 
sulphide,  while  those  of  the  second  remain  dissolved. 
After  the  hydrogen  sulphide  has  separated  all  that  it 
will,  the  precipitate  can  be  filtered  off,  and  then  the 
soluble  sulphides  can  be  separated  by  the  neutrali- 
zation of  the  acid  by  a  base.  By  this  means  a  com- 
plete separation  of  the  two  classes  of  metals  can  be 


204  ELEMENTS   OF  CHEMISTRY. 

effected,   and   such   separations    are    the    basis    of  the 
branch  of  chemistry  termed  analytical  chemistry?1 

The  Hydrogen  Compounds  of  the  Elements  of  the  Nitro- 
gen Family.  The  elements  of  the  nitrogen  family,  with 
the  exception  of  bismuth,  are  capable  of  forming  hy- 
drogen compounds  which  are  constructed  on  the  same 
plan  as  ammonia;  i.e.,  for  one  atom  of  the  charac- 
terizing element  in  each  molecule  of  the  hydrogen 
compound,  we  have  three  atoms  of  hydrogen :  — 

Ammonia  (hydrogen  nitride),  chemical  formula,  NH3. 
Phosphine  (hydrogen  phosphide),  chemical  formula,  PH3  .* 
Arsine  (hydrogen  arsenide),  chemical  formula,  AsII3. 
Stibine  (hydrogen  antomonide),  chemical  formula,  SbH3. 

Like  the  hydrogen  compounds  in  the  other  families, 
those  in  this  diminish  in  stability  as  the  atomic  weight 
of  the  element  entering  into  their  formation  increases. 
Ammonia  is  quite  stable,  while  arsine  and  stibine  are 
both  very  easily  decomposed  into  their  constituent  ele- 
ments by  heating. 

Lastly,  in  the  carbon  family,  we  also  have  five  ele- 
ments, —  carbon,  silicon,  germanium,  tin,  and  lead.  We 
have  here  the  same  changes  with  increasing  atomic 
weight.  Carbon  is  a  not-metal ;  lead,  with  the  highest 
atomic  weight,  is  a  metal.  Only  carbon  and  silicon  are 
capable  of  forming  compounds  with  hydrogen,  and  the 
hydrogen  compound  of  silicon,  while  much  less  stable 
than  methane,  is  formed  according  to  the  same  plan :  — 

Methane,  chemical  formula,  CH4. 
Silicon  hydride,  chemical  formula,  Si  H4 . 

*  The  chemical  symbols  for  one  atom  of  phosphorus,  arsenic,  and 
antimony  are  P,  As,  and  Sb  respectively.  The  symbol  Sb  for  antimony 
is  derived  from  the  Latin  stibium. 


CHEMICAL   NATURE  OF  OTHER   ELEMENTS.      205 

The  few  relationships  which  have  been  mentioned 
will  serve  to  show  what  is  meant  by  the  statement  that 
"  the  elements  are  divided  into  certain  groups  or  fami- 
lies." What  is  true  of  the  few  elements  studied  is  also 
true  of  every  other  element  with  which  we  are  ac- 
quainted. Each  one  of  these  is  a  member  of  a  family 
with  several  representatives  which  are  closely  related 
chemically  and  physically.  In  larger  works  on  chemis- 
try, where  the  characteristics  of  all  of  the  elements  are 
considered,  the  grouping  by  families  forms  the  basis  for 
the  systematic  arrangement  of  such  works. 


APPENDIX. 


PRECAUTIONS  TO  BE    TAKEN  WHILE  WORKING  IN   THE 
LABORATORY. 

BEFORE  entering  upon  laboratory  work  the  pupil  should  read 
and  remember  the  following  cautions  :  — 

Burns,  stains,  and  Jire.  —  Yellow  phosphorus  should  never  be 
handled  except  with  a  pair  of  tongs  or  pincers.  When  exposed 
to  the  air  in  a  warm  room  it  may  take  fire  spontaneously.  If 
touched  by  the  hand  it  will  take  fire.  The  burns  so  produced 
are  extremely  painful,  and  may  become  dangerous  by  reason  of 
phosphorus  poisoning.  Sodium  and  potassium  are  kept  under 
naphtha.  Pieces  larger  than  beans  should  never  be  placed  in 
water ;  and  in  any  event,  a  very  small  piece  should  first  be  tested. 
Sodium  which  has  not  a  clear  and  bright  surface  when  cut, 
should  be  rejected.  In  all  cases  the  outer  coating  of  oxide  should 
be  cut  away  before  placing  the  metal  in  water.  Burns  are  best 
treated  by  covering  the  spot  with  a  solution  of  cocaine  in  sweet 
oil,  and  then  with  an  emulsion  of  lime-water,  glycerine,  and  sweet 
oil.  Nitric  acid  stains  the  skin  yellow.  Where  concentrated,  it 
will  cause  an  ulcer  to  form.  Bromine  stains  the  skin  brown,  and 
unless  instantly  removed  it  will  cause  a  painful  ulcer.  Iodine 
stains  the  skin  dark  violet ;  nitrate  of  silver,  black.  Of  course 
every  precaution  should  be  taken  to  keep  the  above  substances 
from  touching  the  hands  or  face ;  but,  in  case  of  accident,  washing 
with  clean  water  will  be  best  in  the  case  of  nitric  acid  and  bro- 
mine. A  solution  of  sodium  hyposulphite  followed  by  water  will 
remove  iodine.  Concentrated  sulphuric  acid  will  attack  the  skin  ; 
not  so  rapidly,  however,  as  nitric  acid.  In  case  of  an  accident 
this  can  often  be  removed  by  washing  with  water  or  sodium  car- 
bonate solution  before  serious  results  have  followed.  Hot  sul- 
phuric acid  will  instantly  produce  the  most  painful  burns.  Any 

207 


208  ELEMENTS   OF  CHEMISTRY. 

test-tube  in  which  sulphuric  acid  or  anything  else  is  being  heated, 
should  be  held  by  a  test-tube  holder  with  its  mouth  pointing  away 
from  the  manipulator  or  from  any  one  standing  near.  Ether  or  car- 
bon bisulphide  must  not  be  used  within  six  feet  of  a  burning  Bun- 
sen  burner.  These  liquids  take  fire  with  the  greatest  readiness. 
Matches  should  be  kept  in  a  tin  box,  which  is  never  to  be  placed 
in  the  drawer  of  the  desk,  but  should  always  be  kept  outside. 

Inhalation  of  fumes  and  gases.  —  Chemical  experiments  which 
will  develop  poisonous  or  irritating  gases  should  always  be  per- 
formed under  a  hood  with  a  good  draught.*  Chlorine  and  bromine 
attack  the  mucous  membrane  of  the  eyes,  throat,  and  nose. 
Continued  inhalation  will  give  rise  to  bronchial  inflammation. 
Chlorine  or  bromine  will  also  cause  nausea.  If,  by  accident,  the 
pupil  should  take  an  excessive  quantity  of  chlorine  into  the  lungs, 
the  quickest  remedy  is  probably  the  inhalation  of  the  fumes  of 
alcohol.  The  gaseous  oxides  of  nitrogen  are  poisonous,  causing 
violent  headache  and  nausea.  Phosphine,  arsine,  and  stibine  are 
very  poisonous.  Ammonia  is  quite  irritating.  Work  in  which 
these  substances  are  generated  or  used  must  be  done  under  the 
hood.  Sulphuric  acid  should  not  be  heated  to  above  150°  unless 
the  apparatus  is  under  the  hood.  The  acid  will  break  down, 
partly  into  water  and  sulphur  trioxide  ;  the  vapors  of  the  latter 
are  irritating  to  the  lungs.  Liquids  containing  hydrochloric  acid 
or  nitric  acid  should  be  evaporated  under  the  hood.  Sulphuretted 
hydrogen  is  poisonous  and  disagreeable ;  continued  inhalation  of 
even  small  quantities  will  cause  headache,  and  may  have  serious 
results.  It  is,  therefore,  imperatively  necessary,  unless  a  room 
is  especially  provided  in  which  to  generate  this  gas,  that  all  work 
with  hydrogen  sulphide  should  be  performed  under  the  hood. 
Sulphur  dioxide  is  extremely  irritating ;  work  with  this  gas  must 
always  be  done  under  the  hood. 

Explosions Most  accidents  result  from  carelessness  ;  there- 
fore, the  invariable  rule  by  which  the  student  should  govern  him- 
self in  the  laboratory  is,  "  Never  be  careless ;  for  carelessness  may 

*  So  urgent  is  this  rule  that  pupils  should  be  forbidden  even  to  heat 
test-tubes  or  small  evaporating  dishes  with  reagents  which  will  give  off 
fumes  of  hydrochloric  acid,  nitric  acid,  hydrogen  sulphide,  bromine, 
chlorine,  nitric  oxide,  etc.,  unless  they  do  so  under  the  hood.  A  good 
hood  is  as  necessary  as  a  good  burner. 


APPENDIX.  209 

result  in  permanent  disfigurement  or  loss  of  sight."  Hydrogen 
and  oxygen,  hydrogen  and  air,  hydrogen  and  chlorine,  gaseous 
hydrocarbons  and  oxygen,  phosphine  and  oxygen,  or  phosphine 
and  air,  as  well  as  the  other  not  very  stable  hydrogen  compounds 
of  the  riot-metals,  mixed  with  oxygen  or  air,  will  cause  violent 
explosions  when  ignited.  In  generating  these  gases,  extreme 
care  must  be  taken  not  to  bring  a  flame  near  the  exit-tube  of  the 
apparatus  until  the  pupil  is  sure  that  a  brisk  current  of  the  gener- 
ated gas  has  traversed  the  apparatus  for  sufficient  length  of  time 
to  expel  all  air.  No  definite  time  rule  can  be  established,  be- 
cause this  will  vary  with  the  size  of  the  apparatus ;  but,  when 
using  the  ordinary  generating  flasks  of  from  300  to  500  cc.,  the 
pupil  should  wait  at  least  seven  to  ten  minutes.  Chlorate  of 
potassium,  permanganate  of  potassium,  and  similar  powerful  oxidi- 
zers  must  not  be  rubbed  in  a  mortar  when  in  contact  with  sub- 
stances which  are  readily  oxidized  (sugar,  starch,  sulphide  of 
antimony,  sulphur,  phosphorus,  etc.).  Care  must  be  taken  to 
have  all  drying  trains  or  other  apparatus  for  washing  gases  in 
such  a  condition  that  a  current  of  gas  can  pass  through  freely ; 
otherwise,  when  a  gas  is  being  generated,  the  pressure  caused  by 
a  stoppage  may  give  rise  to  a  dangerous  explosion.  Safety-tubes 
must  always  be  open ;  otherwise  they  are  no  longer  safety-tubes, 
for  their  being  stopped  may  cause  an  explosion.  The  openings 
by  which  gases  escape  from  the  generating  apparatus  must  be 
sufficiently  large  to  allow  a  free  current  of  gas  to  flow. 

In  a  well-conducted  laboratory,  desks  and  apparatus  must 
always  be  kept  as  clean  as  possible,  and  reagent  bottles  returned  to 
their  proper  places  as  soon  as  the  occasion  requiring  their  use  is 
over.  Bunsen  burners  can  be  cleaned  by  unscrewing  the  outer 
tube,  and  brushing  the  nipple  with  a  dry,  stiff,  test-tube  brush. 


LABORATORY  EXPERIMENTS. 

Carefully  read  the  laboratory  precautions  on  preceding  pages. 

THE  following  experiments  are  to  be  conducted  in  the 
laboratory  in  connection  with  the  work  on  the  text.  The 
pupil  must  carefully  follow  all  the  directions,  and  answer 
all  questions,  putting  his  observations  and  answers  in  a 
note-book.  Some  of  the  experiments  can  be  performed 
only  by  the  teacher.  These  are  marked  "  Teacher's 
experiments.''  Their  description  is  to  be  given  in  the 
pupil's  note-book  exactly  as  if  they  had 'been  performed 
by  the  pupil  himself. 


1.   The  Thermometer 

The  thermometer  in  general  scientific  use  is  the  centi- 
grade ;  the  one  in  popular  use  in  the  United  States  is  the 
Fahrenheit.  The  usual  thermometer  measures  the  tem- 
perature by  means  of  the  expansion  of  mercury  when  the 
temperature  is  increased,  or  the  contraction  when  it  is  di- 
minished. It  consists  of  a  capillary  tube,  one  end  of  which 
terminates  in  a  bulb.  This  bulb  and  a  portion  of  the 
capillary  tube  are  filled  with  mercury.  The  upper  part  of 
the  tube  is  either  a  vacuum,  or  is  filled  with  nitrogen,  and  its 
tip  closed  by  fusing  the  glass.  The  bulb  is  first  placed  in 
melting  ice,  and  the  position  of  the  mercury  column  is 
marked  as  0°  (in  the  centigrade  thermometer).  The  ther- 
mometer is  then  transferred  to  water  which  is  boiling  under 
a  pressure  of  one  atmosphere,  and  the  point  at  which  the 

211 


212 


ELEMENTS   OF  CHEMISTEY. 


upper  end  of  the  mercury  column  stands  is  marked  100°. 
The  interval  is  divided  into  100  equal  parts,  called  degrees. 
In  the  Fahrenheit  thermometer  the  melting-point  of  ice  is 
marked  32°,  and  the  boiling-point  of  water,  212°.  The  divis- 
ions in  each  thermometer  are  carried  some  distance  below 
0°,  and  these  are  designated  by  the  minus  sign.  The  dia- 
gram, Fig.  1,  shows  the  difference  between  the  centigrade 
and  Fahrenheit  thermometers. 

FAHREHHEIJ. 


BOIL/NCPOINJ 
OF  mifR 

too0 

\      * 

^/20 

MELTIHt, 
P01HT 

1 

1 

OF  ICE  0° 

32" 

17% 

0" 

Fig.  1. 

The  fundamental  difference  between  the  thermometers  is 
that 

100°  Centigrade  =  180°  Fahrenheit, 
or  5°          «  =      9°  " 

The  temperature  centigrade  in  terms  of   Fahrenheit  is 
therefore  given  by  the  following  calculation : 

t°  Centigrade  =  (f£  +  32)°  Fahrenheit, 
where  t°  represents  the  observed  temperature. 


LABOEATOEY  EXPEEIMENTS.  213 

On  the  other  hand,  t°  Fahrenheit  —  32  =  f 1  Centigrade. 
For  temperatures  below  0°  Fahrenheit,  the  formula  for 
change  to  centigrade  is  — 

I  (—  t°  Fahrenheit  +  32)  =  —  t  Centigrade, 
and         I  (—  t°  Centigrade)  —  32  =  —  t  Fahrenheit, 
and  if  f  —  t°  =  32,  then  the  temperature  is  at  0°  Fahren- 
heit. 

In  all  scientific  work  the  metric  system  is  employed 
exclusively.  If  the  pupil  is  not  already  familiar  with  this 
system,  he  should  thoroughly  familiarize  himself  with  it 
before  beginning  work.  The  metric  system  and  the  centi- 
grade thermometer  are  used  in  this  book.  For  a  description 
of  a  barometer  and  its  use,  see  Experiment  36. 

2.   Solution. 

a.  In  a  test-tube  make  a  saturated  solution  of  common 
salt  (sodium  chloride)  in  boiling  water  *  by  adding  more  salt 
than  the  water  will  dissolve.  Allow  the  undissolved  por- 
tion to  settle,  and  pour  off  the  hot,  clear,  supernatant  liquid 
into  a  second  test-tube,  setting  the  latter  aside  to  cool. 
(Why  cool  ?)  Make  a  careful  examination  with  the  aid  of 
a  small  magnifier  of  the  crystals  which  have  formed. 

Repeat,  using  blue  vitriol  (copper  sulphate)  instead  of 
sodium  chloride. 

Repeat  with  potassium  chlorate.  Use  the  same  amount 
of  water  in  each  of  these  experiments,  and  note  the  differ- 
ence in  the  quantities  of  the  three  substances  which  are 
deposited  on  cooling.  - 

Repeat  the  above  with  a  small  piece  of  marble ;  pour  off 
the  water,  and  evaporate  the  remainder  to  dryness  in  a 
small  porcelain  dish  over  a  flame,  or,  better,  on  a  water 
bath.  (Why  use  a  water  bath  ?)  Note  if  any  residue 
is  formed.  Is  marble  soluble  in  water  ? 

*  Distilled  water  should  be  used  in  all  chemical  work. 


214  ELEMENTS   OF  CHEMISTRY. 

6.    Heat  Changes  During  Solution. 

Take  10  c.c.  of  distilled  water  in  a  test-tube  or  small 
beaker,  and  ascertain  the  temperature.  Add  5  grams  of 
sodium  chloride,  and  stir  with  the  thermometer  until  solu- 
tion is  effected.  Again  note  the  temperature. 

Eepeat  with  copper  sulphate  and  with  potassium  nitrate 
(saltpetre).  (Use  a  clean  beaker  and  fresh  water  in  each 
case.) 

(The  lowering  of  temperature  on  solution  of  salts  is  caused  by  the 
absorption  of  heat,  which  is  used  to  produce  the  fluid  condition  from 
the  solid.) 

3.   Water  of  Crystallization. 

a.  Carefully  dry  some  crystals  of  common  salt  (sodium 
chloride)  by  pressing  them  between  filter  paper,  then  place 
the  crystals  in  a  test-tube,  and  heat  in  the  Bunsen  flame. 

Eepeat  with  (b)  crystals  of  sodium  sulphate  (Glauber's 
salt),  (c)  white  vitriol  (zinc  sulphate),  (d)  copper  sulphate. 
What  is  the  difference  between  the  behavior  of  these  sub- 
stances and  that  of  common  salt  ? 

Determination  of  the  water  of  crystallization. 

Put  about  2  gins,  of  copper  sulphate  crystals  in  a 
weighed  and  clean  porcelain  crucible,  and  heat  for  one  hour 
at  225°  in  an  air  bath.  Cool  in  a  desiccator  and  weigh. 
Heat  again  and  weigh,  continuing  the  operation  until  the 
weight  is  constant.  What  is  the  change  in  appearance  of 
crystals  ?  In  weight  ? 

Eepeat  the  same  experiment  with  a  second  sample  of 
copper  sulphate  crystals,  and  then  ascertain  the  per  cent 
of  loss  in  weight  which  the  crystals  have  suffered  in  each 
experiment.  Is  the  result  the  same  in  both  cases  ?  * 

*  In  performing  experiments  like  the  above,  care  must  be  taken  to 
have  good,  clean  chemicals.  The  copper  sulphate  crystals  must  be  fresh 
and  must  not  have  lost  any  of  their  lustre,  otherwise  no  constant  results 
can  be  obtained. 


LABORATORY  EXPERIMENTS.  215 

4.    a.    Efflorescence. 

Expose  to  the  air  for  twenty-four  hours  some  crystals  of 
sodium  carbonate  on  a  dry  watch-glass.  Do  the  same  with 
some  crystals  of  sodium  sulphate.  With  some  crystals 
of  copper  sulphate.  Note  the  result  in  each  case. 

b.    Deliquescence. 

Expose  to  the  air,  as  in  the  above  experiments,  some 
pieces  of  calcium  chloride.  Some  caustic  potash.  Some 
caustic  soda.  Note  the  result  in  each  case. 

c.    Heat  changes  during  solution  of  anhydrous  substances  capable  of 
uniting  with  water  of  crystallization. 

Repeat  the  experiments  under  2  &,  using  10  cc.  of  dis- 
tilled water,  and  dissolving  in  this  (a)  5  grams  of  fused 
calcium  chloride,  (b)  Eepeat  with  5  grams  of  copper 
sulphate  which  has  been  dried  at  200°.  Note  changes  of 
temperature  in  each  case.  Compare  with  the  results  ob- 
tained by  dissolving  copper  sulphate  containing  water  of 
crystallization. 

5.    Solution  of  Gases  in  Liquids. 

a.  Under  the  bell  jar  of  an  air-pump,  place  a  beaker  of  or- 
dinary water  and  exhaust  the  air.     (Teacher's  experiment.) 

b.  Take  a  beaker  half  full  of  water,  place  it  on  a  wire 
netting  covering  the  ring  of  a  retort  stand,  and  heat  gently. 
Note  that  bubbles  of  gas  pass  off  before  the  water  comes 
to  a  boil. 

The  following  law  governs  the  solution  of  gases  in  liquids. 
The  quantity  of  a  given  gas  which  can  be  dissolved  by 
a  fixed  quantity  of  a  liquid  varies  directly  as  the  pressure 
on  that  gas.  This  form  of  solution  is  termed  the  absorp- 
tion of  a  gas  by  a  liquid.  Where  chemical  union  takes 
place  between  the  gas  and  the  solvent,  the  above  law  does 
not  hold  good.  When  the  pressure  is  removed,  the  gas 
escapes  until  the  solution  is  saturated  at  ordinary  pressure. 


216 


ELEMENTS   OF  CHEMISTRY. 


Example :  —  One  cubic  centimetre  of  water  dissolves  1.05 
cubic  centimetres  of  carbon  dioxide  at  one  atmosphere 
pressure,  and  3.15  cubic  centimetres  at  three  atmospheres. 
Ordinary  soda-water  contains  carbon  dioxide  dissolved 
under  pressure.  When  the  pressure  is  removed,  the  gas 
escapes ;  i.e.,  the  liquid  effervesces. 

6.   Filtration  and  Distillation. 

The  proper  arrangement  of  a  filter  in  a  funnel  is  shown 
by  Fig.  2.  The  filter  paper  (unsized  paper)  is  circular  and 
is  folded  twice,  so  as  to  form  a  quad- 
rant. This  is  opened  so  that  one 
thickness  of  paper  is  on  one  side,  and 
three  on  the  other.  The  paper  is  now 
pressed  snugly  into  the  funnel,  moist- 
ened with  water,  and  brought  evenly 
into  place  by  sucking  on  the  stem. 
A  filter  should  never  reach  above  the 
edges  of  the  funnel.  Take  some  pow- 
dered chalk,  suspend  it  in  20  cc.  of 
water,  and  pour  this  on  the  filter. 
Note  if  the  liquid  passing  through  is 
clear.  (That  which  passes  through  is 
termed  the  filtrate,  that  which  remains 
on  the  filter  the  precipitate.) 
Fig.  3  represents  the  ordinary  distilling  apparatus,  com- 
posed of  a  flask,  Z>,  with  the  thermometer,  T,  condenser,  (7, 
and  receiver,  ft.  The  liquid  in  the  flask  is  boiled,  the  vapor 
is  condensed  by  a  current  of  cold  water,  which  is  admitted 
between  the  outer  jacket  and  the  inner  tube  of  the  con- 
denser at  the  lower  opening,  and  which  escapes  into  a 
basin  at  the  upper  opening. 

Distillation. 

a.    Place  in  the  distilling-flask,  which  should  be  of  100 
to  200  c.c.  capacity,  a  solution  of  2  grams  of  copper  sul- 


Fig.  2. 


LAB  OR  A  TOR  Y  EXPERIMENTS. 


217 


phate  in  50  c.c.  of  water.  Replace  the  stopper  with  the 
thermometer,  and  heat  until  about  one-half  of  the  solution 
has  passed  over  into  the  receiver.  Note  the  boiling-point 
of  the  liquid  in  the  flask.  Evaporate  the  contents  of  the 
receiver  to  dryness,  and  do  the  same  with  the  contents  of 
the  distilling-flask. 

(The  contents  of  the  receiver,  after  distillation,  is  termed 
the  distillate.) 

1).  Distil  90  c.c.  of  ordinary  water  until  about  10  c.c. 
remain,  then  add  50  c.c.  more,  without  emptying  the  distil- 
ling-flask, and  repeat  this  operation  four  times.  Now  put 
the  contents  of  the  distilling-flask  into  an  evaporating-dish, 


Fig.  3. 

and  evaporate  to  dryness  on  a  water-bath.  Put  the  distillate 
into  an  evaporating-dish,  and  also  evaporate  on  a  water- 
bath.  What  is  the  difference  between  the  two  waters 
which  you  have  evaporated  ?  What  class  of  substances 
can  be  separated  from  water  by  distillation  ? 

7.    Action  of  Sodium  and  Potassium  on  Water. 
a.    Take  a  clean  piece  of  sodium  as  large  as  a  pea,  care- 
fully remove  the  naphtha  with  a  piece  of  filter  paper,  and 


218 


ELEMENTS   OF  CHEMISTRY. 


throw  the  sodium  into  a  basin  of  water.  Repeat  with  a 
piece  of  potassium.  Compare  the  action  of  potassium 
with  that  of  sodium.  Be  careful  to  stand  aside  at  least 
eight  feet  while  the  action  is  going  on. 

b.    Collecting  the  gases  generated  by  the  action  of  sodium  on  water. 
Fig.  4  shows  a  vessel,  preferably  of  glass  or  of  sheet 
iron,  with  a  capacity  of  at  least  one  litre.     Nearly  fill  this 

vessel  with  water,  and  invert 
over  it  a  small  test-tube  filled 
with  water.  Now  wrap  in  wire 
gauze  a  clean  piece  of  sodium 
as  large  as  a  pea,  and  with  a 
pair  of  forceps  quickly  place  it 
under  the  mouth  of  the  test- 
tube,  or  use  an  inverted  wire- 
gauze  spoon,  as  shown  in  the 
cut.*  When  the  tube  is  full 
of  gas,  place  the  thumb  over 
its  mouth,  then  light  a  splinter 
of  wood,  remove  the  thumb, 
and  quickly  apply  the  flame  to 
the  mouth  of  the  tube.  Taste 
a  drop  of  the  water  left  in  the  trough.  Insert  the  fingers 
into  the  trough,  and  note  the  feel  of  the  water. 

8.     The  Electrolysis  of  "Water. 

The  apparatus  (Fig.  5)  consists  of  a  shallow  glass  vessel 
with  a  wide  mouth,  closed  by  a  water-tight  rubber  stopper. 
Through  the  stopper  pass  two  stout  platinum  wires  about 
two  or  three  centimetres  apart,  and  extending  several  cen- 

*  Care  should  be  taken  to  test  the  sodium  to  be  used  in  any  of  these 
experiments  by  placing  a  small  piece  on  water,  and  then  standing  aside ; 
for  unless  the  metal  is  clean  there  is  great  danger  of  an  explosion. 
Scraps  of  sodium  which  have  been  kept  in  the  laboratory  for  some  time 
should  never  be  used.  The  brown  rind  must  always  be  carefully  removed 
from  the  sodium  before  using. 


Fig.  4. 


LA B  OEA  TOE  Y  EXPERIMENTS. 


219 


timetres  above  and  below  the  stopper.  To  the  lower  ends 
of  the  platinum  wires  connect  two  or  more  cells  of  a  bichro- 
mate battery  by  means  of  insulated  copper  wires.  Fill  the 
glass  vessel  with  distilled  water, 
also  fill  two  tubes  *  with  the  same 
liquid,  and  invert  them  in  the  ves- 
sel so  that  their  mouths  are  over  the 
wires  ;  adjust  the  tubes  in  a  ver- 
tical position  by  means  of  clamps, 
and  turn  on  the  current.  Is  there 
any  action  ?  (See  page  191.)  Now 
add  concentrated  sulphuric  acid  to 
the  water,  drop  by  drop,  until  there 
is  a  satisfactory  development  of  gas 
at  each  pole.  What  gas  collects  at 
the  negative  pole  ?  What  gas  col- 
lects at  the  positive  pole  ? 

When  10  to  15  c.c.  of  gas  has 
collected  at  the  kathode,t  raise  the 
carbon  and  zinc  plates  from  the 
battery  jar,  allow  the  apparatus  to 
stand  for  five  minutes,  and  then 
carefully  read  off  the  volumes  of 
the  two  gases  which  have  collected. 
Now  with  the  thumb  close  the  tube 
over  the  negative  electrode,  remove 
it  from  the  basin,  invert  it,  and 
instantly  apply  a  lighted  taper  to 


Fig.  5. 


*  The  tubes  should  be  divided  into  cubic  centimetres. 

f  The  negative  pole  of  the  battery  is  the  one  connected  with  the  zinc, 
the  positive  pole  is  the  one  connected  with  the  carbon  in  the  cell.  The 
positive  pole  is  termed  the  anode,  the  negative  pole  the  kathode,  and 
the  liquid  which  is  decomposed  is  the  electrolyte.  The  two  platinum 
wires  are  termed  the  electrodes. 


220 


ELEMENTS   OF  CHEMISTRY. 


its  mouth.  Remove  the  tube  over  the  positive  pole  in  the 
same  way,  and  insert  into  it  a  glowing  pine  splinter.  What 
is  the  difference  between  the  two  gases  ?  Did  you  obtain 
exactly  twice  as  much  of  one  gas  as  of  the  other  ?  If  this 
relationship  is  not  exactly  correct,  what  is  the  reason  for 
the  discrepancy  ? 

9.   Preparation  of  Hydrogen  and  Oxygen  for  Laboratory  Use. 

a.   The  preparation  and  collecting  of  hydrogen. 
It  has  been  found  that  hydrogen  is  liberated  by  the  action 
of  certain  substances  termed  acids  (see  pages  45  and  57)  on 
certain  metals.     For  example,  zinc  when  covered  by  dilute 
sulphuric  acid  generates  hydrogen,  while  at  the  same  time 
the  zinc  is  dissolved  by  the  acid,  and  enters  into  the  forma- 
tion of  a  substance  termed  zinc  sulphate.     At  the  present 
time  the  means  by  which  it  is  done  does  not  interest  us  so 
much  as  the  study  of  the  properties  of  the  hy- 
f /{  A        drogen  which  we  can  obtain. 

The  apparatus  for  the  preparation  of  hydro- 
gen is  shown  by  Fig.  6.  It  consists  of  a  heavy 
walled  flask,  into  which  is  fitted  a  rubber  stopper 
with  two  holes.  Into  one  of  these  a  so-called 
safety-tube  is  fitted  (the  curved  tube  with  the 


Fig.  6. 


LABORATORY  EXPERIMENTS.  221 

funnel  top  and  bulb  in  the  middle;  see  figure),  and  into 
the  other  is  inserted  a  glass  tube  bent  at  a  right  angle,  and 
reaching  just  to  the  bottom  of  the  stopper.  When  all  is 
ready,  place  15  grams  of  zinc  in  the  flask,  insert  the  stop- 
per, and  pour  dilute  sulphuric  acid  through  the  safety- 
tube,  adding  more  acid  from  time  to  time  as  occasion 
requires.*  To  purify  the  hydrogen  generated  by  zinc 
and  sulphuric  acid,  pass  it  through  a  wash-bottle  f  con- 
taining a  solution  of  two  grams  of  caustic  potash  in  10 
grams  of  water,  and  through  a  second  one  with  concen- 
trated sulphuric  acid. 

b.   Experiments  with  hydrogen. 

Fill  two  or  three  test-tubes  or  cylinders  with  the  gas, 
over  water,  as  shown  in  the  figure.  Remove  one  of  these 
from  the  water,  mouth  downward,  and  quickly  insert  a 
lighted  taper.  Connect  an  ordinary  clay  pipe  (coated  with 
paraffine  on  the  outside)  with  the  hydrogen  generator,  and 
bring  the  mouth  of  the  pipe  into  some  strong  soap-suds,  to 
which  has  been  added  a  little  glycerine  or  gum  arabic. 
Note  if  the  soap-bubbles  rise  in  the  air.  Is  hydrogen 
very  soluble  in  water  ?  How  would  you  discover  whether 
a  gas  is  very  soluble  in  water  ? 

c.    The  preparation  and  collecting  of  oxygen  for  laboratory  use. 

In  preparing  large  quantities  of  oxygen  for  laboratory 

*  Dilute  sulphuric  acid  is  prepared  by  adding  one  part  of  commercial 
acid  to  six  parts  of  water.  In  diluting  sulphuric  acid,  pour  the  acid  into 
the  water  slowly,  but  do  not  pour  the  water  into  the  acid.  Cool  the 
acid  by  placing  the  flask  in  which  it  is  diluted  under  the  hydrant 
before  using. 

t  A  wash-bottle  consists  of  an  ordinary  wide-mouthed  bottle,  fitted 
with  a  stopper  having  two  holes.  Into  one  hole  of  the  stopper  is  inserted 
a  tube,  bent  at  a  -right  angle,  and  reaching  to  the  bottom  of  the  flask. 
Into  the  other  is  fitted  a  glass  tube  bent  at  a  right  angle,  and  reaching 
just  to  the  bottom  of  the  stopper.  The  gas  enters  through  the  former 
tube,  and  passes  out  through  the  latter.  When  a  liquid  is  placed  in  the 
bottle  the  gas  must  bubble  through  this  liquid,  and  is  washed  by  it. 
(See  Fig.  6.) 


222 


ELEMENTS   OF  CHEMISTRY. 


use,  it  is  not  expedient  to  decompose  water  by  the  electric 
current.  There  is  a  salt-like  body  (chlorate  of  potassium) 
which,  when  heated  to  a  sufficiently  high  temperature, 
gives  off  oxygen. 

The  apparatus  for  the  preparation  of  oxygen  in  large 
quantities,  shown  in  Fig.  7,  consists  of  a  flask  of  200  c.c. 
capacity,  fitted  with  a  stopper  in  which  is  placed  a  glass 
tube  bent  at  two  right  angles.  This  tube  is 
put  into  the  flask  just  to  the  bottom  of  the 
stopper,  and  its  other  end  is  connected  with  a 
safety-bottle.  This  safety-bottle  must  always  be 
interposed  between  the  water- 
trough  in  which  the  gas  is  col- 
lected, and  the  generating-flask, 
in  cases  where  the  latter  is 
heated  to  a  high  temperature. 
By  this  means,  if  the  water 
should  suck  back,  it 
is  collected  in  the 
empty  safety-bottle, 
and  a  dangerous  ex- 
plosion is  avoided. 
The  arrangement  of 
the  safety -bottle  is 
shown  in  the  cut. 
The  oxygen  passes 
from  the  delivery  tube  of  the  safety-bottle,  and  is  collected 
over  water  just  as  hydrogen  is. 

In  the  generating-flask  place  15  grams  of  chlorate  of 
potassium,  connect  the  apparatus,  invert  several  test-tubes 
in  the  water-trough,  and  then  heat  the  chlorate  of  potas- 
sium until  gas  passes  off  with  moderate  rapidity,  and  until 
all  of  the  air  has  been  expelled  from  the  apparatus  and 
safety-bottle.  Now  collect  the  gas  in  the  test-tubes.  Ke- 


Fig.  7. 


LABORATORY  EXPERIMENTS. 


223 


move  one  of  the  tubes,  and  insert  in  it  a  glowing  pine 
splinter.  Repeat  with  a  second  tube,  using  a  small  piece 
of  charcoal  heated  to  redness  and  placed  on  the  end  of  an 
iron  wire  tightly  wrapped  around  it.  Repeat  the  same 
experiment  with  the  soap-bubbles  which  was  made  with 
hydrogen.  Which  gas  is  more  soluble  in  water,  hydrogen 
or  oxygen  ? 

10.  Explosion  of  a  Mixture  of  Hydrogen  and  Oxygen  in  the  Eudiom- 
eter Tube,  Fig.  8.  (Teacher's  Experiment.) 
The  apparatus  in  which  this  explosion  is  performed  is 
termed  a  eudiometer  tube. 
This  instrument  is  a  glass 
tube,  A,  closed  at  one  end, 
and  graduated  in  cubic  cen- 
timetres. It  has  two  plati- 
num wires  inserted  near  the 
closed  tip,  (7,  in  such  a  man- 
ner that  an  electric  spark 
can  pass  from  one  to  the 
other.  This  tube  is  filled 
with  mercury,  and  inverted 
over  a  mercury  trough,  I. 
In  order  to  prove  the  volu- 
metric composition  of  water, 
slant  the  tube  to  one  side, 
and  admit  about  10  c.c.  of 
hydrogen  prepared  and  puri- 
fied as  in  9  a.  Bring  the 
tube  to  a  vertical  position, 
and  make  careful  readings 
of  the  f ollowing :  — 

1.  Volume  of  gas. 

2.  Temperature. 

3.  Height  of  barometer.  Fig.  8. 


224  ELEMENTS   OF  CHEMISTRY. 

4.  Height  of  the  column  of  mercury  in  the  tube  (in 
millimetres). 

Place  the  readings  in  your  note-book.  Now  again  slant 
your  tube,  and  admit  about  7  c.c.  of  oxygen  from  the 
teacher's  gasometer,  or  from  the  apparatus  which  was 
prepared  for  the  generation  of  oxygen.* 

Be  careful  to  run  in  the  oxygen  very  slowly  through  a 
tube  drawn  down  to  a  small  opening,  otherwise  too  much 
will  be  admitted  by  a  sudden  burst  from  the  generator. 
Now  once  more  bring  the  eudiometer  tube  to  a  vertical 
position,  and  note  :  — 

1.  Volume  of  gas. 

2.  Temperature. 

3.  Height  of  barometer. 

4.  Height  of  the  column  of  mercury  in  the  tube. 

Clamp  the  tube  tightly  in  position,  with  its  open  end 
pressed  down  against  a  leather  washer  in  the  bottom  of  the 
mercury  trough.  Now  pass  a  spark  from  an  induction  coil 
or  Leyden  jar  through  the  gases  by  connecting  the  two 
poles  with  the  platinum  wires  in  the  eudiometer.f  After 
the  explosion  raise  the  eudiometer  slightly  from  the 
washer,  and  allow  the  apparatus  to  stand  twenty  minutes 
while  cooling.  Now  note  :  — 

1.  Volume  of  gas. 

2.  Temperature. 

3.  Height  of  the  barometer. 

4.  Height  of  the  column  of  mercury  in  the  tube. 

*  Oxygen  from  a  gasometer  is  pretty  sure  to  contain  nitrogen.  It  is 
therefore  better  to  prepare  fresh  oxygen  from  potassium  chlorate.  Be 
sure  that  the  gas  has  run  through  the  generating-apparatus  for  a  suffi- 
cient length  of  time  to  expel  all  air,  before  collecting  in  the  eudiometer 
tube.  - 

t  Not  infrequently  the  eudiometers  come  to  the  laboratory  with  the 
ends  of  the  wires  so  near  together  that  the  spark  will  not  be  large 
enough  to  ignite  the  gases;  if  such  is  the  case,  force  the  ends  apart  care- 
fully with  a  long  glass  rod. 


L Alton ATOR r  EXPERIMENTS. 


225 


Recalculate  all  the  above  observations  so  that  the  gas 
volume  in  each  is  reduced  to  0°  and  760°  mm.  of  the 
barometer.* 

If  10  c.c.  (corrected)  of  hydrogen  and  7  c.c.  of  oxygen 
were  admitted  to  the  eudiometer,  then  10  c.c.  of  hydrogen 
will  unite  with  5  c.c.  of  oxygen  to  form  water  (2  volumes 
of  hydrogen  to  1  of  oxygen),  and  2  c.c.  of  oxygen  will 
remain  unaltered.  The  residual  gas  may 
be  tested  for  oxygen  in  the  usual  manner. 
It  is  well  to  repeat  the  experiment,  this 
time  employing  an  excess  of  hydrogen. 

11.  Proof  that  Two  Volumes  of  Hydrogen  with 
One  of  Oxygen  form  Two  Volumes  of  "Water 
Vapor.  Fig.  9.  (Teacher's  Experiment.) 

The   apparatus  consists,   essentially,  of 
a  eudiometer  surrounded  by  a  glass  jacket 
joined  to  the  eudiometer  by  means 
of  a    tightly   fitting   triple    bored 
stopper.     The  three   holes  in  the 
stopper  are  for  the  following  pur- 
poses :  The  one  in  the  mid- 
dle   is    for   the    eudiometer 
tube;     the    second    (a),    for 
the  admission  of  steam  by 
means  of  a  glass  tube  bent 
with  a  right  angle ;  and  the 
third  for  the  exit  of  the  con- 
densed water  by  means  of  a 
similarly  bent  glass  tube.  Fig  Q 

*  For  the  formulae  necessary  to  recalculate  gases  to  standard  condi- 
tions, and  for  the  reasons  for  such  formulae,  see  pages  68,  69,  and  70.  The 
experiments  numbered  36,  37,  and  38  can,  if  desired  by  the  teacher,  be 
performed  in  this  place  before  the  pupil  does  the  work  of  recalculating 
the  gas  volumes  noted  in  his  observations  of  the  above  experiment. 


226  ELEMENTS   OF  CHEMISTRY. 

Fill  the  eudiometer  with  perfectly  clean,  dry  mercury, 
carefully  removing  every  bubble  of  air,*  and  invert  it  in  a 
cylinder  of  mercury  about  30  centimetres  in  depth.  Now 
raise  the  eudiometer  until  its  mouth  is  just  below  the  sur- 
face of  the  mercury  in  the  trough,  and  admit  about  15  c.c. 
of  the  mixture  of  hydrogen  and  oxygen  obtained  from  the 
electrolysis  of  water,  f  Now  pass  a  jet  of  steam  into  the 

jacket  until  the  apparatus 
is  heated  to  100°  C,  and 
note  the  volume  of  the  gas 
as  well  as  the  height  of  the 
column  of  mercury  in  the 
eudiometer  tube  above  that 
in  the  trough.  Lower  the 
eudiometer  tube  and  jacket 
so  that  the  open  end  is  well 
under  the  mercury,  wrap  a 
towel  round  the  top  of  the 
mercury  trough,  and  ex- 
plode the  gases  as  in  the 

Fig.  10.  .  . 

previous  experiment.    Now 

adjust  the  tube  so  that  the  height  of  the  column  of  mer- 
cury in  it  is  the  same  as  it  was  before,  and  make  a  second 
reading  of  the  volume  of  gas,  taking  care  that  the  tem- 


*  Remove  bubbles  of  air  by  nearly  filling  the  tube  with  mercury, 
closing  the  open  end  with  the  thumb,  and  slowly  passing  a  large  bubble 
of  air  back  and  forth  through  the  entire  length  of  the  tube. 

t  A  simple  apparatus  for  generating  this  mixture  of  oxygen  and 
hydrogen  is  shown  by  Fig.  10.  This  consists  of  a  wide-mouthed  bottle 
of  100  c.c.  capacity,  closed  with  a  single  bored  rubber  stopper.  In  this 
stopper  are  inserted  two  stout  platinum  wires,  hammered  flat  at  the 
ends,  and  in  the  opening  is  placed  a  glass  tube  of  one  or  two  millimetres 
internal  diameter,  bent  as  in  the  figure,  and  reaching  just  to  the  lower 
edge  of  the  stopper.  Almost  fill  the  bottle  with  dilute  sulphuric  acid, 
insert  the  stopper,  connect  with  the  battery,  wait  for  some  minutes  until 
the  gas  has  passed  off,  and  then  collect  in  the  eudiometer. 


LA  B  OR  A  TOR  Y   EX  L  'MR  U1EN  TS. 


227 


perature  is  still  at  100°  C.  What  is  the  ratio  between 
the  volumes  of  gas  before  and  after  explosion  ?  Allow 
the  tube  to  cool,  and  observe  the  remaining  volume 
of  gas. 

12.   Burning  of  Hydrogen*  in  Oxygen,  and  Formation  of  "Water  by 
this  Means.     (Teacher's  Experiment.)     Fig.  11. 

The  apparatus  consists  of  a  vessel  constricted  in  the 
middle,  and  is  fitted  with  a  glass  stopcock  delivery-tube. 
A  wide  globe  funnel  with  a  long  stem  is  placed  in  the 
upper  opening  of  this  vessel.  The  zinc  is 
placed  in  the  middle  globe,  and  dilute  sul- 
phuric acid  is  added  from  above  until  the 
apparatus  is  filled  to  about  the  middle  of 
the  funnel.  On  opening  the  stopcock,  the 


Fig.  11. 

acid  ascends  to  the  metal.  On  closing  it,  the  generated 
hydrogen  once  more  expels  the  acid  from  the  central  globe. 
In  this  way  the  metal  can  be  indefinitely  kept  out  of 

*  The  hydrogen  needed  must  be  available  in  a  current  which  is  easily 
regulated.  For  this  purpose  it  is  best  prepared  in  a  so-called  Kipp's  gas- 
generator.  A  description  of  this  generator  is  given  above,  and  it  is 
shown  at  the  extreme  right  of  the  cut. 


228  ELEMENTS    OF  CHEMISTRY. 

contact  with  the  acid,  and  need  only  be  acted    on    by  it 
when  the  stopcock  is  opened.* 

A  regular  current  of  hydrogen  such  as  is  necessary  to 
maintain  a  small  flame,  cannot  be  obtained  if  the  gas  is 
purified  by  passing  through  wash-bottles.  For  this  reason 
so  called  U-tubes  (shown  in  the  centre  figure)  must  be 
substituted.  The  contents  of  these  purifying  tubes,  count- 
ing from  the  generator,  are  — 

1.  Pieces  of  brick  moistened  with  a  solution  of  potas- 
sium permanganate. 

2.  Coarse  pieces  of  solid  caustic  potash. 

3.  Granular  (anhydrous)  calcium  chloride. 

The  exit  tube  of  No.  3  terminates  in  a  platinum  tip  of  a 
diameter  not  more  than  one  millimetre,  made  from  a  roll 
of  platinum  foil,  and  fused  into  the  open  end  of  the  glass 
tube.  The  wash-bottle  at  the  extreme  left  contains  con- 
centrated sulphuric  acid  to  dry  the  oxygen  which  is  passed 
in  from  left  to  right.  Both  the  hydrogen  and  oxygen  which 
are  to  be  admitted  into  the  vertical  cylinder  are  therefore 
perfectly  dry  and  pure. 

Manipulation:  Remove  the  platinum  tipped  tube  from 
the  vertical  cylinder,  and  start  the  hydrogen  generator. 
After  waiting  at  least  ten  minutes,  when  all  the  air  has 
been  expelled  from  the  train  and  apparatus,  ignite  the  hy- 
drogen at  the  tip,  and  regulate  the  current  so  that  a  flame 
of  not  more  than  one  centimetre  in  length  is  obtained.  In 
the  meantime  expel  all  the  air  from  the  vertical  cylinder 
by  a  steady  stream  of  oxygen  from  the  teacher's  gasometer. 
Now  pass  the  jet  of  burning  hydrogen  upward  through  the 
central  opening  in  the  stopper,  so  that  it  is  just  above  the 
place  where  the  oxygen  enters.  What  collects  on  the  sides 
of  the  cylinder  ?  Taste  the  liquid  which  soon  passes  off 
through  the  exit  tube  at  the  upper  end.f 

*  If  necessary  the  hydrogen  can  be  generated  as  described  in  experi- 
ment 9  a. 

t  See  foot-note  on  page  25. 


LABORATORY  EXPERIMENTS.  229 

13.  Examination  of  the  Substance  "which  remains  in  the  Water 
after  it  has  been  acted  upon  by  Sodium. 

Cut  a  piece  of  sodium  as  in  7a,  and  throw  it  into  a  small 
evaporating-dish  containing  150  c.c.  of  water.  Stand  aside 
until  the  action  is  over,  and  until  all  the  sodium  has  dis- 
appeared. Now  add  a  second  piece,  and  wait  as  before. 
Continue  the  operation  until  four  pieces  have  been  added. 
Evaporate  the  solution  as  far  as  possible  on  a  water-bath, 
transfer  the  small  quantity  of  liquid  which  is  left  to  a 
small  porcelain  crucible,  and  dry  in  an  air-bath  at  150°. 
Note  the  appearance  of  what  is  left'.  Has  it  any  resem- 
blance to  sodium  ?  Is  it  soluble  in  water  ?  Make  a  very 
dilute  solution  of  a  portion  of  it,  and  taste  a  drop.  Com- 
pare this  taste  with  that  of  a  very  dilute  solution  of 
caustic  soda  which  you  obtain  from  the  side-table.  Com- 
pare the  feel  of  the  solution  with  that  of  a  solution  of 
caustic  soda. 

14.    Decomposition  of  the   Caustic    Soda   obtained  by  the   Action  of 
Sodium  on  "Water.     Proof  that  This  Substance  contains  Hydrogen. 

a.  A  mixture  of  sodium  and  caustic  soda  when 
heated  will  develop  hydrogen,  thereby  furnishing 
absolute  proof  that  only  a  portion  of  the  hydrogen 
is  expelled  from  water  when  it  is  acted  on  by 
sodium ;  but  this  experiment  probably  can  be  per- 
formed successfully  only  by  the  teacher.  Dry 
some  caustic  soda  completely  by  fusing  it  in  an 
iron  crucible  over  a  Bunsen  flame.  Allow  to  cool, 
powder  the  caustic  soda,  and  place  about  three 
grams  in  a  test-tube  of  so-called  infusible  glass. 
Add  one-half  gram  of  clean  sodium,  and  fit  into 
the  test-tube  a  single-bored  rubber  stopper  which  is 
provided  with  a  glass  tube  drawn  out  to  a  point,  so 
as  to  make  a  burner  (Fig.  12).  Now  gently  heat 
the  sodium  (holding  the  test-tube  by  a  holder) 
until  the  metal  is  melted.  Gradually  increase  the  Fig,  12. 


230  ELEMENTS   OF   CHEMISTRY. 

temperature,  and  light  the  hydrogen  at  the  tip  of  the 
burner.  This  is  a  conclusive  proof  that  caustic  soda 
contains  hydrogen.  It  has  been  shown,  therefore,  that 
water  is  first  changed  by  the  action  of  sodium  so  that  a 
part  of  the  hydrogen  is  set  free,  leaving  caustic  soda  ; 
and  then  sodium,  acting  on  caustic  soda,  sets  free  the 
remainder.  The  hydrogen  in  water  is  therefore  divisible 
into  two  parts.  The  experiments  which  prove  that  these 
are  two  equal  parts  are  too  difficult  to  perform  here;  it 
is  sufficient  to  know  that  .1  gram  of  sodium,  acting  on 
water,  sets  free  48.22  c.c.  of  hydrogen;  and  when  the 
caustic  soda  formed  from  this  amount  of  sodium  is  care- 
fully dried  and  heated  with  sodium,  a  second  48.22  c.c. 
of  hydrogen  are  liberated.  The  hydrogen  in  water  is 
therefore  divisible  into  two  equal  parts. 

15.   Inauguration  of  Chemical  Action  by  Heat.     Kindling 
Temperature. 

(Perform  these  experiments  under  the  hood.) 

Place  five  drops  of  carbon  bisulphide  in  a  dry  test-tube, 
and  warm  with  the  hand  until  the  tube  is  filled  with  the 
vapors  of  the  liquid,  then  insert  in  the  mouth  of  the  test- 
tube  a  glass  rod  which  has  previously  been  warmed  in  the 
flame  of  a  Bunsen  burner. 

Cut  a  piece  of  phosphorus  half  the  size  of  a  pea  (phos- 
phorus must  always  be  cut  under  water,  and  handled  with 
forceps),  dry  it  quickly  by  pressing  it  between  sheets  of 
filter  paper,  transfer  it  to  a  deflagrating  spoon,  and  bring 
it  gradually  toward  the  flame.  Repeat  with  red  phos- 
phorus. Sulphur.  Carbon. 

What  is  the  cause  of  the  explosion  in  a  eudiometer  tube 
when  the  electric  spark  is  passed  from  one  platinum  wire 
to  the  other,  as  in  Experiment  10  ? 

16.    Preparation  of  Hydrogen  Chloride. 

Arrange  an  apparatus  as  shown  in  Fig.  13.     The  gen- 


LABOR  A  TOE  Y  EXPERIMENTS. 


231 


erating-flask  should  have  a  capacity  of  about  500  cubic 
centimetres.  The  wash-bottle  contains  concentrated  sul- 
phuric acid. 

Place  in  the  generating-flask  25  grams  of  sodium  chloride, 
pour  upon  it  50  c.c.  of  dilute  sulphuric  acid  (2  volumes  of 
concentrated  sulphuric  acid  to 
1  volume  of  water),  and  heat 
gently.     Collect  four  small  jars 
of  the  gas  by  displacement  of 
air,*  covering  them  with  a  glass 
plate  as  soon  as  filled.     Collect 
the  remainder  of  the  gas  in  a 
small  beaker  of  water. 


17.    Properties  of  Hydrogen 
Chloride. 

Invert  one  jar  of  gas  in  a 
vessel  of  water.  Taste' a  drop 
of  the  solution.  Blow  the 
breath  across  the  mouth  of 
a  second  jar.  Insert  into  an 
other  jar  a  burning  splinter. 


Fig.  13. 


18.  a.  Preparation  of  Sodium  Amalgam.  (Under  the  Hood.) 
To  prepare  sodium  amalgam  place  500  grams  of  clean, 
dry  mercury  in  a  large  clay  crucible,  and  cover  with  a 
piece  of  sheet  iron.  Cut  5  grams  of  clean  sodium  into 
pieces  the  size  of  a  hickory  nut,  and  place  them  in  the  cru- 
cible. 4Fo  start  the  reaction,  heat  a  few  grams  of  mercury 
in  a  test-tube,  slightly  raise  the  cover  of  the  crucible,  pour 
in  the  mercury,  and  instantly  withdraw  the  hand.  A  reac- 

*  Gases  which  are  specifically  heavier  than  air  may  be  collected  by 
passing  the  delivery  tube,  through  which  the  gas  is  flowing,  to  the  bottom 
of  the  jar;  gases  specifically  lighter  than  air  are  collected  in  an  inverted 
jar  by  passing  the  delivery  tube  to  the  top  of  the  jar.  (See  Fig.  31.) 


232 


ELEMENTS    OF  CHEMISTRY. 


tion,  accompanied  by  a  flash  of  light,  will  occur.  Stand 
aside,  so  as  not  to  inhale  the  fumes  of  the  mercury.  When 
the  reaction  is  finished,  stir  the  amalgam  with  an  iron  wire, 
allow  it  to  cool,  and  place  it  in  a  stoppered,  wide-mouthed 
bottle. 

b.    Decomposition  of  hydrogen  chloride  by  sodium.     Fig.  14. 

Take  a  glass  tube  30  cm.  in  length  and  15  mm.  in  diam- 
eter, sealed  at  one  end.     Divide  this  tube  by  means  of  two 
a       rubber  rings  slipped  over  it.     One  rubber  ring  is 
placed  at  a  distance  from  the  sealed  end  repre- 
sented by  10  c.c.  of  the  capacity  of  the  tube,*  and 
the   other  is   placed  half-way  between  this  ring 

and  the  open  end  of  the 
tube.  Have  ready  a 
small  glass  test-tube,  c, 
of  10  c.c.  capacity,  com- 
pletely filled  with  so- 
dium amalgam.  Now 
completely  fill  the  large 
tube  with  hydrogen  chlo- 
ride, displacing  the  air, 
as  shown  in  the  cut.  The 
hydrogen  chloride  must 
be  dried  by  passing  it 
through  a  wash-bottle 
containing  sulphuric  acid.  When  the  tube  is  filled,  pour 
in  the  sodium  amalgam,  quickly  cover  the  mouth  of  the 
tube  with  the  thumb,  and  bring  every  part  of  the  gas  in 
contact  with  the  amalgam  by  repeatedly  inverting  the  tube. 

*  This  10  c.c.  of  the  tube  is  to  be  filled  with  sodium  amalgam ;  hence 
the  volume  of  hydrogen  chloride  which  will  be  left,  after  introducing 
the  sodium  amalgam,  will  be  represented  by  the  interval  between  the 
ring  at  10  c.c.  and  the  remainder  of  the  tube. 


Fig.  14. 


LAB  OR  A  TOE  Y  EX  PER  IMENTS. 


233 


Finally,  place  the  open  end  of  the  tube  in  a  deep  cylinder, 
under  water,  and  remove  the  thumb.  Lower  the  tube  in 
the  water  so  that  the  level  within  and  without  is  the  same 
(shown  by  b  in  the  figure).  What  is  the  relation  between 
the  volume  of  gas  remaining  and  that  which  was  originally 
present  ?  Now  place  the  thumb  over  the  mouth  of  the 
tube,  take  it  from  the  water,  invert  it,  remove  the  thumb, 
and  instantly  apply  a  lighted  taper.  The  pupil  can  con- 
vince himself  that  mercury  alone  has  no  action  on  hydro- 
gen chloride,  by  repeating  the  above  experiment,  using 
10  c.c.  of  pure  mercury  instead  of  sodium  amalgam. 
What  decomposes 'the  hydrogen  chloride  ? 

19.    Decomposition  of   Hydrochloric  Acid   by  Means  of   the  Electric 
Current.     Fig.  15.     Hood! 

The  apparatus  consists  of  a  letter-U- 
shaped  tube,  which  is  connected  at  the 
centre  of  the  curve  with  an  upright  fun- 
nel tube,  serving  for  the  introduction  of 
the  liquid.  The  two  arms  terminate  in 
glass  stopcocks.  The  electrodes  must  be 
made  of  the  carbon  which  is  used  in  arc 
electric  lights,  because  platinum  is  attacked 
during  the  electrolysis  of  hydrochloric  acid. 
These  carbon  poles  must  extend  well  up 
into  the  tubes,  and  must  be  protected,  ex- 
cept at  the  tips,  by  a  glass  tube  slipped 
over  them,  and  made  water-tight  by  pour- 
ing in  melted  paraffine  between  the  carbon 
and  the  tube.  This  apparatus  is  designed 
for  teachers'  use. 

A  simple  apparatus  for  pupils  can  be 
made  similar  to  that  shown  by  Fig.  5, 
the  platinum  wires  being  replaced  by  two 
cylinders  of  carbon,  which  are  connected  Fig.  15, 


234 


ELEMENTS   OF  CHEMISTRY. 


with  the  battery  by  copper  wires.  Fill  either  apparatus 
with  a  saturated  solution  of  commou  salt  to  which  has  been 
added  one-tenth  of  its  volume  of  a  saturated  solution  of 
hydrogen  chloride  in  water.  When  the  current  is  turned 
on,  a  gas  will  be  evolved  at  the  negative  pole.  When  the 
tube  over  this  electrode  is  full  of  gas,  remove  it,  and  test 
for  hydrogen.  The  gas  at  the  positive  electrode  will  not 
be  apparent  for  some  time,  because  it  is  soluble,  to  a  cer- 
tain extent,  in  the  liquid.  After  a  time  it,  too,  will  appear. 
What  is  its  color  ?  Odor  ?  Apply  a  lighted  taper  to  the 
mouth  of  the  tube  in  which  this  gas  is  collected.  Pill  a 
second  tube,  and  place  in  it  a  small  prece  of  .moist  red 
calico.  If  the  electric  current  is  allowed  to  run  long 
enough,  equal  volumes  of  the  two  gases  will  be  evolved 
in  equal  lengths  of  time.  Compare  this  result  with  that 
obtained  when  water  is  electrolyzed.  What  does  this  ex- 
periment and  the  preceding  one  teach  you  in  regard  to  the 
composition  of  hydrogen  chloride  by  volume  ? 

20.  Formation  of  Hydrogen  Chloride  from  Hydrogen  and  Chlorine. 
Volumetric  Composition  of  Hydrogen  Chlorine.  Fig.  16.  Teach- 
er's Experiment. 

The  apparatus  consists  of  two  tubes,  each 
about  15  cm.  in  length.  These  two  tubes  are 
connected  by  a  stopcock,  which  is  so  arranged 
that  either  one  of  the  tubes  can  be  made  to 
communicate  with  the  outside  air,  while,  by 
turning  it  through  45°,  the  two  tubes  can  be 
made  to  communicate  exclusively  with  each 
other,  the  opening  to  the  outside  being  closed. 
This  kind  of  stopcock  is  termed  a  three-way 
stopcock;  its  arrangement  is  shown  by  Fig. 
17.  The  two  tubes  are  drawn  out  into  nar- 
row openings  at  the  two  outer  extremities, 
and  are  so  selected  as  to  be  of  equal  volume. 


Fig.  18. 


LABORATORY  EXPERIMENTS.  235 

Manipulation.  Connect  the  three-way  stopcock  at  A 
with  an  apparatus  furnishing  dry  chlorine.  This  is  done 
by  the  apparatus  described  in  Experiment  21&.  Turn  the 
stopcock  so  that  the  chlorine  will  pass 
through  one  of  the  tubes,  and  allow  the 
gas  to  enter  until  all  air  is  expelled. 
Now  seal  the  tip  of  the  tube  in  a  Bunsen 
name,  and  turn  the  stopcock  so  that  the 
chlorine  tube  is  closed  and  the  second 
tube  is  open  to  the  atmosphere.  Fill 
this  tube  with  dry  hydrogen  (prepared 
as  in  Experiment  9&),  and  when  all  air 
is  expelled,  seal  this  tip  also  in  the 
Bunsen  flame.  Now  turn  the  stopcock 
so  that  the  two  tubes  will  communicate  with  each  other 
while  they  are  both  shut  to  the  outside  air.  Allow  tne 
apparatus  to  stand  in  the  daylight  for  twenty-four  hours. 
Has  the  color  of  the  chlorine  disappeared  ?  Scratch  one  of 
the  tips  with  a  file,  bring  it  into  a  vessel  containing  dry 
mercury,  and  break  the  tip  with  a  pair  of  pincers.  Does 
the  mercury  rise  in  the  tube  ?  What  does  this  teach  regard- 
ing the  volume  of  gas  remaining  after  the  experiment,  as 
compared  with  that  before  ?  Hydrogen  chloride,  as  we 
have  learned,  is  extremely  soluble  in  water,  while  hydrogen 
and  chlorine  are  not.  Remembering  this,  we  can  easily 
ascertain  whether  the  hydrogen  and  chlorine  have  all  been 
used  to  form  hydrogen  chloride,  by  pressing  a  piece  of 
rubber  over  the  broken  tip  of  the  apparatus,  and  transfer- 
ring it  to  a  vessel  of  water. 

If  hydrogen  chloride  has  been  formed,  and  if  all  the 
hydrogen  and  all  the  chlorine  have  united,  the  water  will 
rush  in  and  completely  fill  the  apparatus.*  Is  this  the 

*  Of  course,  if  care  has  not  been  taken^o  expel  all  the  air  from  the 
tubes,  this  air  will  remain  after  the  experiment,  and  the  result  will  be 
inaccurate. 


236 


ELEMENTS  OF  CHEMISTRY. 


case  ?  What  does  the  experiment  teach  as  regards  the 
relative  volumes  of  hydrogen  and  chlorine  which  unite  to 
form  hydrogen  chloride  ?  As  regards  the  relation  between 
the  volumes  of  hydrogen  and  chlorine  used,  and  the  volume 
of  hydrogen  chloride  produced  ?  Compare  these  results 
with  those  obtained  in  Experiments  10  and  11. 

21.    a.   Preparation  of    Chlorine  by  the  Action  of   Oxygen  on 
Hydrogen  Chloride.     Fig.  18. 

It  is  not  expedient  to  prepare  chlorine  for  laboratory  use 
by  the  electrolysis  of  hydrochloric  acid.  Chlorine  can  be 
prepared  by  decomposing  hydrogen  chloride  by  oxygen, 
the  oxygen  uniting  with  the  hydrogen  of  the  hydrogen 
chloride,  while  the  chlorine  is  set  free.  This  change  takes 
place  only  at  a  high  temperature.  Prepare  an  apparatus,  A, 


Fig.  18. 

for  generating  hydrogen  chloride  as  described  in  Experi- 
ment 16,  with  this  difference,  that  the  wash-bottle,  7?,  is 
fitted  with  a  triple-bored  rubber  stopper.  The  wash-bottle 
contains  sulphuric  acid  in  order  to  dry  the  gases.  The 
three  holes  are  for  the  following  purposes  :  — 

1.  For  the  admission  of  hydrogen  chloride. 

2.  For  the  admission  of  oxygen. 

3.  For  the  exit  of  the  mixed  gases  into  an  iron  tube,  E, 
which  is  placed  in  a  gas   furnace  (shown  in  the   cut)  so 
that  it  can  be  heated  to  redness. 


LABORATORY  EXPERIMENTS.  237 

By  this  means  a  mixture  of  dry  oxygen  and  hydrogen 
chloride  is  obtained  and  passed  through  the  heated  tube. 
The  bubbles  of  hydrogen  chloride  and  of  oxygen  passing 
through  the  wash-bottle  should  be  of  equal  number  in  the 
same  interval  "of  time.  The  ends  of  the  iron  tube  are 
fitted  with  cork  stoppers,  into  which  pass  the  entrance  and 
exit  tubes  for  the  gases.  The  joints  are  made  secure  by 
a  coating  of  plaster  of  Paris.  Between  the  iron  tube  and 
the  water-trough  beyond  is  placed  a  safety  bottle,  C,  such 
as  is  described  in  Experiment  9c.  When  the  apparatus  is 
ready,  the  tube  is  heated  to  redness  in  the  furnace,  and  the 
mixture  of  hydrogen  chloride  and  oxygen  is  passed  through. 
Finally  pass  the  gases  under  a  tube,  D,  inverted  in  a 
beaker  of  water.  rfoes  the  odor  of  chlorine  become  appar- 
ent ?  Test  the  water  for  chlorine  by  placing  in  it  a  small 
piece  of  red  calico.  Is  it  bleached  ? 

This  experiment  shows  us  that  although  we  can  obtain 
chlorine  by  the  action  of  oxy gen  on  hydrogen  chloride,  the 
method  is  not  practical  for  laboratory  use.  However,  we 
need  not  use  gaseous  oxygen  for  this  purpose;  for  it  is 
known  that  many  compounds  which  contain  oxygen  give 
off  that  oxygen  readily  under  certain  circumstances,  and 
that  such  oxygen,  when  it  is  just  in  the  act  of  being 
liberated  from  chemical  compounds,  readily  decomposes 
hydrogen  chloride,  setting  free  chlorine,  and  forming  water. 
Such  an  oxygen-containing  compound  is  black  oxide  of 
manganese. 

b.    Preparation  of   chlorine  from   black  oxide   of   manganese 
and  hydrochloric  acid.      (Experiment  under  Hood.) 

Arrange  an  apparatus  as  shown  by  Fig.  13,  Experiment 
16.  In  the  flask  place  50  grams  of  black  oxide  of  man- 
ganese, and  pour  over  it  through  the  safety-tube  enough  of 
a  concentrated  solution  of  hydrogen  chloride  in  water  to 
cover  the  oxide.  In  the  wash-bottle  put  sulphuric  acid, 


238  ELEMENTS   OF  CHEMISTRY. 

and  collect  the  gas  which  passes  off  by  displacement  of  air, 
as  you  did  hydrogen  chloride.  Color  of  gas  ?  Place  in 
one  of  the  jars  a  piece  of  dry  colored  calico.  Place  in  a 
second  jar  a  piece  of  moist  colored  calico.  Odor  of  gas  ? 
(Do  not  inhale  more  than  a  very  small  quantity  of 
chlorine.  Pan  the  air  above  the  cylinder  of  chlorine 
with  the  hand,  and  get  the  odor  of  the  gas  while  you  are 
at  some  distance.)  Invert  one  of  the  jars  in  a  basin  of 
water.  Is  chlorine  soluble  in  water  ?  As  soluble  as  hydro- 
gen chloride  ?  Pass  chlorine  into  a  beaker  of  water  until 
you  have  a  saturated  solution.  Color  and  odor  of  solution  ? 
Does  it  bleach  colored  calico  ? 

22.   Decomposition  of  "Water  by  Chlorine  in  the  Sunlight.     Fig.  19. 
Take  a  tube  40  cm.  long,  bent  as  shown  in  the  figure, 
and  closed  at  the  upper  end  of  the  long  arm.     Completely 
fill  this  tube  with  solution  of  chlorine  in  water,  invert  it  as 
shown  in  the  figure,  pour  off  about  20  c.c.  of  the  solution, 
and  clamp  the  tube  in  an  upright  position.    Cover  the  open 
end  with  a  test-tube,  and  leave  it  in  the  sun- 
light  for    some   days.      When   about  20   c.c. 
of  gas  has  been  collected,  close  the  open  end 
of  the  tube  with  the  thumb,  invert  it  so  that 
the  gas  ascends  to  the  bend,  then  once  more 
bring  it  to  an  upright  position,  allowing  the 
gas  to  pass  into  the  small  arm.      Now  remove 
the  thumb,  and  quickly  bring  a  glowing  pine 
splinter  into  the  tube.     Taste  the  liquid    re- 
maining in  the  tube.     In  this  case,  what  action 
has  the  chlorine  on  the  water  ?      Why   does 
Fj    1g  chlorine  bleach  moist   colored  calico  and  not 

dry  calico  ? 
23.   Action  of  Hydrochloric  Acid  on  Metals. 

a.    In  a  test-tube  place  a  little  sodium  amalgam,  and  pour 
over  it  some  hydrochloric  acid.     Apply  a  lighted  taper  to 


LABORATORY  EXPERIMENTS.  239 

the  gas  which  passes  off,  or,  better,  arrange  the  test-tube  as 
shown  by  Fig.  12,  and  light  at  the  tip.  After  the  action 
has  ceased,  pour  off  the  liquid  from  the  mercury,  and  evapo- 
rate to  crystallization  on  a  water-bath.  Examine  the  crys- 
tals under  a  magnifying-glass.  In  what  experiment  have 
you  seen  similar  crystals  ?  What  substance  is  formed  ? 

b.  In  a  test-tube  place   some   mercury,  and   pour  on  it 
hydrochloric  acid.     Is  there  any  action  ?     In  the  above 
experiment,  what  acted  on  the  hydrochloric  acid  ? 

c.  Repeat   a,   using    a   few   pieces   of    granulated    zinc 
instead    of    sodium    amalgam.      If    necessary,    filter   the 
solution  which  is  formed,  and  evaporate. 

d.  Repeat  a  with  iron  filings. 

e.  Repeat  a  with  a  piece  of  magnesium  wire. 

24.    Action  of   Hydrochloric  Acid  on  the  Oxides  of   Metals. 

a.  In  a  test-tube  place  a  small  piece  of  quicklime  (cal- 
cium oxide).     Pour  on  it  dilute  hydrochloric  acid.     Evap- 
orate the  solution,  and  examine  as  in  22a. 

b.  Repeat,  using  zinc  oxide. 

c.  Repeat,  using  oxide  of  iron. 

d.  Repeat,  using  magnesium  oxide.     In  the  last  three 
cases    determine    whether   water   alone    has    any   solvent 
action. 

25.    Action  of   Hydrochloric  Acid  on  the  Hydroxides  of   Metals. 

a.  In  a  test-tube  place  a  small  piece  of  caustic  soda 
(sodium  hydroxide),  dissolve  it  in  water,  and  place  a  drop, 
taken  out  with  a  glass  rod,  on  a  piece  of  paper  dyed  with 
red  litmus.  Now  add  dilute  hydrochloric  acid  to  the  liquid 
in  the  test-tube  until  a  drop  turns  a  strip  of  paper  dyed 
with  blue  litmus  to  red.*  Now  evaporate  as  in  22a,  and 
examine  the  crystals. 

*  Acids  turn  blue  litmus  (a  vegetable  dye)  to  red ;  alkalies,  like 
caustic  soda,  turn  red  litmus  to  blue. 


240  ELEMENTS   OF  CHEMISTRY. 

b.  In  a  test-tube  place  a  small  piece  of  quicklime  (cal- 
cium oxide),  and  add  a  few  drops  of  water.     Wait  a  few 
minutes.     Pour  on  10  c.c.  of  water,  shake  well,  and  filter. 
Take  a  drop  of  the  filtrate,  and  put  on  a  piece  of  red  lit- 
mus paper.     Now  add  hydrochloric  acid,  and  proceed   as 
in  a. 

c.  Obtain  some  magnesium  hydroxide,  and  add   hydro- 
chloric acid  until  solution  is  effected.     Evaporate  as  in  a. 

d.  Repeat,  using  zinc  hydroxide. 

e.  Repeat,  using  hydroxide  of  iron. 

26.    Use  of  Indicators. 

Solutions  which  contain  alkalies  (sodium  hydroxide,  po- 
tassium hydroxide,  calcium  hydroxide)  are  termed  alkaline. 
The  reverse  of  an  alkaline  solution  is  an  acid  solution. 
We  are  acquainted  with  a  number  of  colored  substances 
which  assume  colors  varying  with  the  solution,  whether  it 
be  alkaline  or  acid.  Such  substances  are  termed  indica- 
tors. Litmus  (Experiment  25),  as  we  have  seen,  is  blue  in 
the  presence  of  alkalies,  and  red  in  the  presence  of  acids. 
It  is  obvious  that,  with  the  aid  of  litmus,  we  can  tell 
whether  a  solution  is  acid  or  alkaline ;  but  there  are  cer- 
tain objections  to  this  vegetable  dye.  These  objections  are 
that  it  is  changed  in  color  not  only  by  the  alkaline  hydrox- 
ides, but  by  a  number  of  salts  as  well.  For  this  reason 
litmus  has  largely  been  superseded  by  a  number  of  other 
indicators,  the  most  convenient  of  which  is  a  dye  made 
from  coal-tar,  and  called  methyl  orange. 

Dissolve  one-half  a  gram  of  methyl  orange  in  25  c.c.  of 
water.  To  a  little  of  this  solution  in  a  test-tube  add  two 
or  three  drops  of  hydrochloric  acid.  To  this  acid  solution 
add  a  dilute  solution  of  caustic  soda  until  the  color  changes. 
At  the  point  where  the  color  changes,  the  solution  is  said 
to  be  neutral ;  i.e.,  there  is  neither  hydrochloric  acid  nor 


LAB  OR  A  TOR  Y  EXPERIMENTS. 


241 


sodium  hydroxide  present,  for  the  acid  has  neutralized  the 
hydroxide  to  form  sodium  chloride  and  water.  Repeat, 
using  potassium  hydroxide.  Repeat,  using  a  solution  of 
calcium  hydroxide. 


27. 


Neutralization  of  Known  Quantities  of  an  Acid  by 
vice  versa. 


,  ana 


Liquids  are  most  accurately 
measured  by  means  of  burettes. 
(Fig.  20.)  A  burette  is  a  glass 
tube  graduated  into  TT¥  c.c.,  open 
above,  closed  below  either  with 
a  rubber  tube  closed  with  a 
pinchcock  and  terminating  in 
a  glass  tip  drawn  to  a  point, 
or  with  a  glass  stopcock.  By 
opening  the  stopcock,  liquid 
runs  out,  and  its  amount  can 
be  accurately  measured  by  the 
graduation  above. 

a.    To  make  a  solution  of  alkalies. 

1.  Dissolve  4  grams  of  sodium 
hydroxide,  weighed  as  accurately 
as  possible,  in  500  c.c.  of  distilled 
water.     Place  the  solution  in  a 
tightly    stoppered     bottle,    and 
keep  for  future  use. 

2.  Make  and  bottle  a  solution  of  the  same  quantity  of 
potassium  hydroxide  in  the  same  amount  of  water. 

&.    Solution  of  hydrochloric  acid. 

Measure  accurately  5  c.c.  of  hydrochloric  acid  (1  part  of 
pure  concentrated  hydrochloric  acid  to  1  part  of  water), 
and  dilute  to  250  c.c.  Preserve  this  solution  for  future 
use  in  a  stoppered  bottle. 


Fig.  20. 


242  ELEMENTS   OF  CHEMISTRY. 

Have  two  burettes ;  fill  one  with  solution  a  1,  the  sec- 
ond with  solution  b,  and  cover  the  open  ends  by  slipping 
over  them  two  inverted  test-tubes.  Clamp  the  burettes  in 
an  upright  position,  as  shown  in  the  cut. 

In  a  clean  beaker  place  10  c.c.  of  solution  b,  add  a  few 
drops  of  a  solution  of  methyl  orange  (Experiment  26),  and, 
after  noting  accurately  the  quantity  of  solution  in  the 
burette  containing  solution  a  1,  add  this,  drop  by  drop,  to 
the  acid  in  the  beaker,  at  the  same  time  stirring  with  a 
glass  rod.  Stop  adding  solution  a  1,  at  the  point  where 
the  color  of  the  methyl  orange  just  changes  permanently, 
and  note  the  number  of  cubic  centimetres  of  the  alkali 
which  have  been  used.  What  amount  of  sodium  hydrox- 
ide, in  grams,  does  this  represent  ?  Repeat  with  a  second 
10  c.c.  of  acid,  and  note  whether  the  two  results  agree.  If 
they  do,  pour  out  the  alkali  solution  from  the  burette, 
wash  the  instrument  carefully  with  distilled  water,  dry  it, 
and  fill  with  solution  a  2.  Take  10  c.c.  of  the  acid  solu- 
tion, and  proceed  as  before.  What  amount  in  grams  of 
potassium  hydroxide  was  used  to  neutralize  10  c.c.  of  the 
acid  ?  Is  this  amount  the  same  as  the  quantity  of  sodium 
hydroxide  used  to  neutralize  the  same  quantity  of  acid  ? 
If  it  is  not,  what  is  the  ratio  between  the  amounts  of 
sodium  hydroxide  and  potassium  hydroxide  which  are 
used  to  neutralize  the  same  quantity  of  acid  ? 

c.    Preparation  of  a  solution  containing  a  known  quantity  of 
hydrochloric  acid. 

Into  a  distilling-flask,  arranged  as  in  Fig.  3,  place  15 
grams  of  sodium  chloride ;  add  a  cold  mixture  of  40  grams 
of  sulphuric  acid  and  80  grams  of  water.  Arrange  the 
condenser  so  that  it  terminates  in  an  ordinary  pair  of  wash- 
bottles  (shown  by  Fig.  6),  each  containing  about  10  c.c.  of 
water.  Place  the  thermometer  tightly  in  the  distilling- 


LABORATORY-  EXPERIMENTS.  243 

flask,  and  distil  until  one-half  of  the  liquid  has  passed 
over.  Allow  it  to  cool,  add  another  80  grams  of  water  to 
the  distilling-flask,  and  distil  again.  All  the  hydrochloric 
acid  will  now  have  passed  over  with  the  distillate.  Take 
the  contents  of  the  wash-bottles,  carefully  wash  them  into 
a  graduated  cylinder,  and  dilute  to  500  c.c.  Fifteen  grams 
of  sodium  chloride  produce  9.18  grams  of  hydrochloric  acid, 
therefore  the  500  c.c.  of  solution  contain  9.18  grams  of 
hydrochloric  acid.  Take  10  c.c.  of  this  solution,  and  neu- 
tralize with  solution  a  1.  With  solution  a  2.  How  much 
by  weight  of  sodium  hydroxide  is  neutralized  by  1  gram  of 
hydrochloric  acid  ?  How  much  of  potassium  hydroxide  ? 
What  is  the  ratio  between  the  amounts  of  sodium  hydrox- 
ide and  of  potassium  hydroxide  which  will  neutralize  1 
gram  of  hydrochloric  acid?  Compare  this  result  with 
those  obtained  in  this  Experiment,  b.  The  quantities  of 
sodium  hydroxide  and  of  potassium  hydroxide  which  will 
exactly  neutralize  the  same  amount  of  hydrochloric  acid 
are  said  to  be  equivalent. 

28.    a.   Burning  of  Sulphur  in  Oxygen  and  the  Product  formed. 

Fill  a  32-oz.  wide-mouthed  bottle  with  oxygen.  Place 
about  .5  grams  of  sulphur  in  a  deflagrating-spoon  passed 
through  a  piece  of  sheet  tin  large  enough  to  cover  the 
mouth  of  the  bottle.  Ignite  the  sulphur  in  the  flame  of  a 
burner,  and  lower  it  into  the  bottle.  When  combustion  is 
completed,  remove  the  spoon,  cover  the  jar  with  a  glass 
plate,  and  allow  it  to  stand  for  a  few  minutes.  Color  of 
gas  ?  Lower  a  burning  pine  splinter  into  the  jar.  Moisten 
a  piece  of  blue  litmus  paper,  attach  it  to  the  glass  cover, 
and  allow  it  to  stand  in  the  bottle.  Changes  of  color  ? 
Test  the  odor  of  the  gas  as  you  did  with  chlorine.  (Ex- 
periment 21&.)  The  product  of  this  combustion  is  termed 
sulphur  dioxide, 


244  ELEMENTS   OF  CHEMISTRY. 

b.    Preparation  of  sulphur  dioxide  for  laboratory  use. 

It  is  not  expedient  to  prepare  sulphur  dioxide  for  labora- 
tory use  by  the  above  method.  In  order  to  obtain  sulphur 
dioxide  in  large  quantities/ advantage  is  taken  of  the  fol- 
lowing fact :  — 

Sulphuric  acid  is  composed  of  hydrogen,  sulphur,  and 
oxygen.  When  it  is  heated  with  certain  metals  it  gives 
up  a  portion  of  this  oxygen,  much  in  the  same  way  as 
black  oxide  of  manganese  gives  up  its  oxygen  to  hydro- 
chloric acid  (see  Experiment  21&).  What  is  left  of  the 
sulphuric  acid  after  it  has  lost  a  portion  of  its  oxygen 
then  breaks  down  into  sulphur  dioxide  and  water,  the 
sulphur  dioxide  being  a  gas.  The  best  metal  to  use  for 
this  purpose  is  copper. 

Arrange  an  apparatus  as  in  Experiment  16,  Fig.  13.  In 
the  generating-flask  place  25  grams  of  copper  shavings,  and 
add  100  c.c.  of  concentrated  sulphuric  acid  through  the 
safety-tube.  Connect  all  parts  of  the  apparatus  (the  wash- 
bottle  should  contain  concentrated  sulphuric  acid),  and  heat 
by  means  of  a  Bunsen  burner  until  gas  begins  to  come  off. 
At  this  point  lower  the  flame  until  you  obtain  a  regular 
and  slow  evolution  of  gas.  Collect  the  evolved  gas  by  dis- 
placement of  air  in  four  small  jars,  which  you  cover  with 
glass  plates  as  soon  as  filled,  and  pass  the  excess  of  gas  into 
a  beaker  of  water.  Odor  of  gas  ?  Compare  with  odor  of  gas 
obtained  from  burning  sulphur.  Invert  one  of  the  jars  in  a 
vessel  of  water.  Is  the  gas  very  soluble  in  water  ?  Lower 
a  lighted  splinter  into  another  jar.  Pour  into  one  of  the 
jars  a  little  blue  litmus  solution,  and  allow  it  to  stand  for 
a  short  time.  Obtain  a  red  rose,  dip  it  in  water,  and  sus- 
pend it  in  a  jar  of  sulphur  dioxide  for  some  time.  A  solu- 
tion of  sulphur  dioxide  is  easily  changed  back  to  sulphuric 
acid  by  means  of  oxygen.  To  a  few  drops  of  sulphur 
dioxide  solution,  in  a  test-tube,  add,  drop  by  drop,  a  solu- 


LAB  OEA  TOR  Y  EXPERIMENTS. 


245 


tion  of  chlorine  in  water  until  the  odor  of  sulphur  dioxide 
disappears.  What  is  the  means  by  which  chlorine  is  able 
to  add  oxygen  to  sulphur  dioxide  ? 

29.    Changing  of  Sulphur  Dioxide  to  Sulphur  Trioxide  by  Means  of 

Oxygen. 

Arrange  an  apparatus  as  shown  in  Fig.  21. 
The  generating-flask  is  the  same  as  in  Ex- 
periment 28 ;  but  the  wash-bottle  contains  a 
triple-bored  rubber  stopper,  arranged  as  in 
Experiment  21,  Fig.  18.      Into  one  of  the 
holes  of  the  wash-bottle  pass  a  tube 
connected  with  the       sulphur  dioxide 
generator;  into  the        second    pass    a 


tube  from  the  oxygen  gasometer.  By  this  means  a  mixture 
of  sulphur  dioxide  and  oxygen  is  obtained  in  the  wash-bot- 
tle. This  mixture  passes  from  the  third  tube  into  a  second 
wash-bottle  and  then  into  a  tube  of  infusible  glass,  in  the 
middle  of  which  is  blown  a  bulb,  into  which  is  stuffed,  with 
a  glass  rod,  a  little  platinized  asbestos.*  The  farther  end 
of  this  bulb  tube  is  connected  with  a  small  distilling-flask, 

*  Platinized  asbestos  is  asbestos  coated  with  a  very  fine  deposit  of 
platinum.  It  has  been  found  that  many  chemical  reactions  between 
gases  take  place  much  more  readily  if  they  are  passed  over  heated,  finely 
divided  platinum,  such  as  is  deposited  on  platinized  asbestos.  The  rea- 
son for  this  is  that  the  platinum  condenses  the  gases  on  its  surface,  and 
gives  them  a  more  intimate  contact.  Platinized  asbestos  is  furnished  by 
dealers  in  chemicals. 


246  ELEMENTS   OF  CHEMISTRY. 

by  which  is  surrounded  by  snow  or  ice,  and  the  exit  tube  of 
which  dips  under  mercury.*  The  mercury  constitutes  a 
valve  for  the  escape  of  gases,  while  at  the  same  time  it  pre- 
vents moisture  from  getting  back  into  the  apparatus.  When 
all  is  ready,  pass  the  mixture  of  sulphur  dioxide  and  oxygen 
slowly  through  the  bulb  tube,  and  heat  the  platinized  as- 
bestos by  a  Bunsen  burner.  The  sulphur  trioxide  which 
is  formed  is  condensed  in  the  small  receiving-flask.  After 
the  apparatus  has  been  running  about  half  an  hour,  stop 
the  inflow  of  gases,  and  remove  the  receiving-flask.  Is  sul- 
phur trioxide  a  solid  or  a  liquid?  If  a  solid,  warm  the  flask 
slightly  with  the  hand.  Does  the  sulphur  trioxide  melt  ? 

30.  Formation  of  Sulphuric  Acid  from  Sulphur  Trioxide  and  "Water. 
Surround  a  receiver  containing  sulphur  trioxide  with 
cold  water,  and  carefully  add  water,  drop  by  drop,  until  all 
is  liquid.  Dilute  a  few  drops  of  this  liquid  with  a  good 
deal  of  water  in  a  test-tube.  Taste  a  drop.  Add  a  few 
drops  to  a  solution  of  methyl  orange.  Place  a  drop  on 
a  strip  of  blue  litmus  paper.  Take  a  few  drops  of  sul- 
phuric acid  from  your  reagent  bottle,  dilute  as  above,  and 
repeat  these  tests.  Evaporate  any  excess  of  water  in 
the  sulphur  trioxide  by  placing  the  solution  in  a  small 
evaporating-dish  on  a  water-bath.  Compare  the  appear- 
ance of  the  remainder  after  evaporation  with  ordinary 
sulphuric  acid,  and  preserve  it  until  the  next  experiment 
is  finished. 

31.    Dehydrating  Action  of  Sulphuric  Acid. 

a.  Put  a  little  sugar  in  a  test-tube,  and  pour  on  it  just 
enough  concentrated  sulphuric  acid  to  cover.  Set  it  aside 
in  the  test-tube  rack.  Put  some  concentrated  sulphuric 
acid  in  a  test-tube,  place  in  it  a  small  piece  of  wood,  and 
allow  it  to  stand.  The  effect  on  the  wood  and  on  the 

*  The  shape  and  relative  size  of  the  distilling-flask  is  shown  by  a  in 
the  figure. 


LABORATOR 

sugar  is  due  to  the  fact  that  sulphuric*acM*Tras  a  great 
tendency  to  take  up  water.  Sugar  and  the  greater  portion 
of  the  wood  contain  hydrogen  and  oxygen  in  exactly  the 
proportions  necessary  to  form  water.  When  acted  on  by 
sulphuric  acid  a  reaction  takes  place,  and  the  water  is 
absorbed  by  the  acid.  Eepeat  the  above,  using  the  sul- 
phuric acid  formed  by  the  action  of  water  on  sulphur 
trioxide. 

b.    Changes  of  temperature  when  sulphuric  acid  is  diluted. 

Kepeat  Experiment  4c,  gradually  adding  concentrated 
sulphuric  acid  to  water,  and  stirring  it  with  the  thermom- 
eter. Note  changes  in  temperature.  Place  some  concen- 
trated sulphuric  acid  in  a  test-tube,  and  surround  with  a 
mixture  of  snow  and  salt.  Does  the  acid  freeze  ?  Weigh 
a  small  stoppered  flask,  then  add  10  c.c.  of  sulphuric  acid, 
and  again .  weigh ;  pour  out  the  acid,  and  wash  well  with 
water.  Now  place  10  c.c.  of  water  in  the  flask,  and  weigh. 
What  is  the  specific  gravity  of  the  acid  ? 

32.   Action  of  Dilute  Sulphuric  Acid  on  Metals. 
Repeat  Experiment  23&,  #,  c,  d,  and  e,  using  dilute  sul- 
phuric acid  instead  of  hydrochloric  acid  (1  part  concen- 
trated acid  to  20  parts  of  water).     What  substances  are 
formed  ?     What  gas  passes  off  ? 

33.    Action  of  Sulphuric  Acid  on  the  Oxides  of  the  Metals. 
Eepeat  Experiment  24a,  b,  c,  d,  using  dilute  sulphuric 
acid   instead  of  hydrochloric   acid.     What   substances  are 
formed  ? 

34.    Neutralization  of   Sulphuric  Acid  by  Potassium  Hydroxide  and 
Sodium  Hydroxide. 

Use  burettes,  as  in  Exp.  27,  Pig.  20.  Measure  accu- 
rately 10  c.c.  of  sulphuric  acid  (containing  1  volume  of 
pure,  concentrated  sulphuric  acid,  specific  gravity  1.84,  to 


248  ELEMENTS   OF  CHEMISTRY. 

6  volumes  of  water*),  and  dilute  this  to  500  c.c.     Put  it 
in  a  stoppered  bottle,  and  preserve  it. 

a.  Place  50  c.e.  of  this  solution  in  a  beaker,  add  a  few 
drops  of  methyl  orange  solution  (Experiment  26),  and  run 
in  from  a  burette  a  solution  of  sodium  hydroxide  prepared 
exactly  as  in  Experiment  27a,  1.     After  about  30  c.c.  have 
been  added,  begin  to  add  your  alkali  cautiously,  drop  by 
drop,  until  the  solution  becomes  neutral.     Evaporate  the 
solution  on  a  water-bath  until  crystals  separate.     Examine 
these  carefully  under  a  magnifying-glass.     Dry  some  of 
the  crystals  with  filter  paper,  place  them  in  a  test-tube, 
and  heat  cautiously.     Compare  the  result  with  that  ob- 
tained in  Experiment  3b.     Finally  heat  the  crystals  to  the 
full  heat  of   a  Bunsen  burner,  and  test  the  water  which 
has  collected  on  the  upper  part  of  the  test-tube  with  blue 
litmus  paper. 

b.  Eepeat  a,  using  a  solution  of  potassium  hydroxide 
prepared  as  in  Experiment  27a,  2. 

Are  the  quantities  of  sodium  hydroxide  and  potassium 
hydroxide  necessary  to  neutralize  the  same  quantity  of 
acid  equal?  If  not,  what  is  the  ratio  between  the  two? 
Is  this  ratio  the  same  as  that  obtained  in  Experiment  27 
in  neutralizing  hydrochloric  acid  ? 

c.  Repeat  a,  placing  in  the  beaker  100  c.c.  of  the  acid, 
and  adding  just  as  much  sodium  hydroxide  as  was  found 
necessary  to  completely  neutralize  50  c.c.     Evaporate  the 
solution  on  the  water-bath,  examine  the  crystals,  and  heat 
as  in  a.     Test  the  moisture  which  collects  on  the  sides  of 
the  test-tube  with  blue  litmus  paper.     Is  it  acid  ?     What 
is  the  difference  between  the  salt  formed  in  this  experi- 
ment  and   the   one   in   a  ?     If   you   had   used   the   same 
amount  of  sulphuric  acid  in  each  case,  what  would  be  the 

*  A  large  quantity  of  this  acid  can  be  prepared  by  the  teacher,  and 
kept  for  use. 


LABORATOB  Y  EXPERIMENTS. 


249 


ratio  between  the  amount  of  sodium  hydroxide  used  iri  a 
and  in  c. 

d.    Repeat  c,   with   a   solution    of  potassium    hydroxide 
prepared  as  in  Experiment  27 'a,  2. 


35.    Comparison  of  the   Results   obtained  with  Sulphuric  Acid   and 
Those  with  Hydrochloric  Acid. 

If  the  sulphuric  acid  which  you  used  was  accurately  pre- 
pared, 10  c.c.  contained  .0511  gram  of  sulphuric  acid. 
How  much  sodium  hydroxide  by  weight  was  necessary  to 
neutralize  completely  one  gram  of  sulphuric  acid  ?  How 
much  potassium  hydroxide  ?  How  much  sodium  hydroxide 
reacted  with  one  gram  of  sulphuric  acid  in  c  ?  In.  d  ? 
What  is  the  ratio  between  the  quantities  of  sodium  hydrox- 
ide and  potassium  hydroxide  necessary  to  neutralize  one 
gram  of  sulphuric  acid  ?  Is  this  ratio  the  same  as  that 
between  the  sodium  hydroxide  and  potassium  hydroxide 


BASE. 

HYDROCHLORIC 
ACID. 

SULPHURIC 
ACID. 

WEIGHT  OF  HYDROXIDE 
IN  THE  SOLUTION  WHICH 

WAS   USED. 

1O  c.c. 

2O  c.c. 

lOc.c. 

2O  c.c. 

for  1O  c.c. 
of  Sulphu- 
ric Acid. 

for  1O  c.c. 
of  Hydro- 
chloric 
Acid. 

c.c. 

c.c. 

c.c. 

c.c. 

grams. 

grams. 

Sodium 
hydroxide. 

Potassium 
hydroxide. 

WEIGHT  OF  HYDROXIDE  NECESSA 
HYDROCHLORIC  ACID. 

RY  TO  NEUTRALIZE  ONE  GRAM  OF 
SULPHURIC  ACID. 

Sodium 
hydroxide. 

Potassium    > 
hydroxide. 

Ratio,— 

sodium  hydroxide : 
potassium  hydroxide  :  1  :  x. 


Ratio,— 

sodium  hydroxide : 
potassium  hydroxide  :  1  :  x. 


250 


ELEMENTS   OF  CHEMISTRY. 

necessary  to  neutralize  one  gram  of  hydrochlo- 
ric  acid  ?  Concordant  results  can  be  obtained 
in  the  above  experiments  only  by  the  most 
careful  work.  Each  determination  should  be 
made  at  least  twice,  so  as  to  insure  accuracy. 
The  table  on  preceding  page  will  be  found  ex- 
pedient in  tabulating  results. 


Fig.  22. 


36.    Construction  of  a  Barometer. 

a.  Seal  one  end  of  a  glass  tube  one  metre 
in  length  and  about  one  cm.  in  internal  diam- 
eter. Nearly  fill  this  tube  with  dry  mercury, 
close  with  the  thumb,  and  remove  small  air- 
bubbles  by  passing  a  larger  bubble  to  and  fro 
in  the  tube.  Now  entirely  fill  the  tube,  again 
close,  and  invert  in  a  vessel  of  mercury. 
Clamp  the  tube  in  an  upright  position,  and 
measure  with  a  metre-stick  the  distance  be- 
tween the  level  of  the  mercury  in  the  lower 
vessel  and  the  level  in  the  tube. 

1).  The  barometer  shown  by  Fig.  22  is  con- 
structed on  the  following  principle.  The  tube 
is  curved  so  that  the  shorter  arm,  a,  takes  the 
place  of  the  lower  vessel  described  above,  the 
mercury  being  held  in  place,  with  its  lower 
level  at  a,  by  the  pressure  of  the  atmosphere. 
The  tube  is  filled  with  mercury,  carefully 
heated  until  all  small  air-bubbles  are  expelled, 
and  then  inverted.  At  the  upper  level  of  the 
mercury,  and  extending  150  mm.  above  and 
below  it,  is  placed  a  portion  of  a  metre  scale, 
the  0  point  of  which  is  given  by  a  movable 
mark  at  a.  The  scale  has  attached  to  it  a 
sliding  vernier,  b,  so  that  the  level  of  the 


LABORATORY  EXPERIMENTS,  251 

mercury  can  be  read  to  ^  of  a  millimetre.  As  the  height 
of  the  barometer  varies,  so  must  the  level  of  the  mercury 
above  and  below  vary.  However,  as  the  measurement 
must  always  begin  at  the  same  point,  provision  is  made 
for  adjusting  the  level  of  the  lower  mark  so  that  it  cor- 
responds to  the  lower  level  of  the  mercury.  When  the 
vernier  is  placed  at  the  upper  level,  the  corresponding  mark 
on  the  scale  gives  the  total  height  of  the  barometer,  c  rep- 
resents a  thermometer  attached  to  the  instrument. 

c.  As  water  is  specifically  much  lighter  than  mercury, 
it  must  be  true  that  the  atmosphere  can  support  a  higher 
column  of  water  than  of  mercury.  In  order  to  prove  this, 
cover  the  mercury  vessel  in  this  Experiment,  a,  with  about 
an  inch  of  water,  and  then  carefully  raise  the  barometer 
tube  until  its  mouth  is  just  above  the  level  of  the  mercury, 
but  below  the  level  of  the  water.  The  mercury  flows  out, 
the  water  takes  its  place,  and  completely  fills  the  tube. 

37.     Proof   That   a   Given   Volume   of    Gas   varies   Inversely   as  the 
Pressure  on  It. 

The  apparatus  is  arranged  as  in  Fig.  23,  1.  It  consists 
of  a  tube  about  one  and  one-third  metres  in  length  and  20 
cm.  internal  diameter.  It  is  open  at  both  ends,  and  curved 
so  as  to  form  a  short  arm  of  about  30  cm.  in  length.  The 
short  arm  is  closed  with  a  rubber  stopper,  single-bored,  into 
which  is  fitted  an  absolutely  tight  glass  stopcock.  The 
tube  is  fastened  to  a  board,  on  which  are  marks  indicating 
distance,  in  inches  or  centimetres. 

Manipulation :  Open  the  glass  stopcock,  and  carefully 
pour  in  clean,  dry  mercury  through  the  long  arm,  until  the 
level  in  both  arms  stands  at  0  (Fig.  23,  1).  Now  close  the 
stopcock.  Note  the  volume  of  confined  air,  which  obvi- 
ously is  under  a  pressure  of  one  atmosphere.  Note  also 
the  height  of  the  barometer.  Again  pour  mercury  into  the 
long  arm,  until  the  differ ence  in  the  level  of  the  mercury  is 


252 


ELEMENTS   OF  CHEMISTRY. 


equal  to  one-half  the  observed  barometric  height  (Fig. 
23,  2).  The  confined  air  is  now  subjected  to  a  pressure  of 
one  and  one-half  atmospheres.  What  is  the  ratio  between 
the  present  volume  and  the  original  volume  of  air  ?  Again 
add  mercury  until  the  gas  is  subjected  to  a  pressure  of  two 
atmospheres  (Fig.  23,  3).  What  is  now  the  volume  of 
gas  ?  What  is  the  ratio  between  this  and  the  original  vol- 


Fig.  23. 

ume  ?  Of  course,  if  a  sufficiently  long  tube  is  taken,  this 
experiment  can  be  extended  so  as  to  include  3  or  4  atmos- 
pheres, and  it  can  be  repeated  with  other  gases  (hydrochlo- 
ric acid,  sulphur  dioxide,  oxygen,  and  hydrogen).  Other 
gases  can  be  filled  in  by  attaching  the  gas  generator  to  the 
open  stopcock,  while  at  the  same  time  enough  mercury 


LA  B  OR  A  TOR  Y  EXPERIMEN  TS. 


253 


Fig.  24. 


is  placed  in  the  tube  to  bring  both  sides  to  0.  The  gas 
will  then  be  forced  in,  will  bubble  out,  and  through  the 
mercury,  and  expel  the  air. 

38.    Influence  of  Vapor  Pressure  on  the  Volume  of  Gas 
enclosed  in  a  Barometric  Tube. 

a.  Arrange  a  barometer  as  in  Experiment  36  a, 
marking  the  height  of  the  mercury  column  with 
a  rubber  ring.  Slip  under  the  open  mouth  of 
the  barometer  tube  the  end  of  a  curved  pipette 
(Fig.  24)  filled  with  water,  the  upper  end  of 
which  you  have  closed  with  the  finger.  Remove 
,  .  the  finger,  and  blow  in- 

to the  upper  end  of  the 
pipette,  so  as  to  force 
about  10  drops  of  water 
into  the  barometer. 
What  is  the  level  of 
the  mercury  after  introducing  the 
water  ?  Note  the  temperature,  and 
measure  in  millimetres  the  differ- 
ence between  the  original  height  of 
mercury  and  the  present.  Warm 
the  tube  at  its  upper  end,  where 
the  water  is,  by  holding  the  hand 
round  it  for  a  few  minutes.  Warm 
it  in  a  cloth  dipped  in  hot  water. 
Note  change  in  the  height  of  the 
barometer  in  each  case. 

b.    Repeat   &,   using   alcohol   in- 
stead of  water. 
c.    Kepeat  a,  using  ether  instead  of  alcohol. 
Fig.  25  represents  four  barometer  tubes.     Tube  a  is  an 
ordinary  barometer ;  tube  b  contains  water  vapor ;  tube  c, 
alcohol ;  and  tube  d,  ether. 


Fig.  25. 


254  ELEMENTS   OF  CHEMISTRY. 

d.    Expansion  of  gases  by  heat. 

Repeat  Experiment  36a,  with  the  difference  that  in  fill- 
ing the  barometer  tube  you  allow  5  c.c.  of  air  to  remain. 
Mark  the  height  of  mercury  in  the  tube  by  a  rubber  ring. 
Now  warm  the  enclosed  gas  with  the  hand.  With  a  cloth 
dipped  in  hot  water.  To  perform  this  experiment  accu- 
rately, so  as  to  ascertain  the  degree  of  expansion  with  each 
degree  of  temperature,  is  too  elaborate  for  this  work.  The 
pupil  must  remember,  arbitrarily,  that  gases  expand  ^1^  for 
each  degree  of  increase  in  temperature.  Using  the  for- 
mula on  page  70,  ascertain  what  the  volume  of  25  c.u  of 
air  would  be  at  760  mm.  pressure,  if  this  air  is  measured 
at  743  mm.  What  is  the  volume  of  25  c.c.  of  air  at  0°  and 
760  mm.  if  the  air  is  measured  at  22°  and  760  mm.  ? 
Twenty-five  c.c.  of  air,  containing  water  vapor,  and  en- 
closed in  a  tube  over  mercury,  are  under  the  following 
conditions :  — 

Temperature  =  30°. 

Barometer  =  725  mm. 

Height  of  mercury  column  =  425  mm. 

What  is  the  volume  of  the  dry  gas  at  0°  and  760  mm.  ? 

e.  Fill  a  glass  tube  of  100  c.c.  capacity,  graduated  in  half 
c.c.,  one-fourth  full  of  mercury,  and  invert  it  in  a  cylinder 
of  mercury  about  30  c.m.  in  depth.  Lower  the  tube  so  that 
the  level  of  the  mercury  without  and  within  is  the  same. 
Under  what  pressure  is  the  enclosed  volume  of  gas  ?  Note 
accurately  the  enclosed  volume  of  gas  and  the  height  of 
the  barometer.  Eaise  the  tube  a  few  centimetres,  clamp 
it  in  this  position,  and  allow  it  to  stand  for  five  minutes. 
Again  read  the  volume  of  gas,  and  measure  carefully  the 
height  of  the  column  of  mercury  in  the  tube  above  that  in 
the  cylinder. 

Repeat,  raising  the  tube  still  higher. 


LABORATORY  EXPERIMENTS. 


255 


If  v  =  the  first  volume, 

vl  =  the  second  volume, 
B  =  barometric  height, 
h  =  height  of  column  of  mercury  in  tube, 
show  that  v  :  v1  : :  B  —  h  :  B. 

39.  Preparation  of  Nitrogen  from  the  Atmosphere.  Fig.  26. 
The  apparatus  consists  of  a  tube  of  infusible  glass,  with 
a  bulb  blown  in  the  middle.  This  bulb  is  filled  with  copper 
filings.  At  the  right  this  tube  is  connected  by  means  of  a 
capillary  glass  tube  with  a  large  bottle  fitted  with  a  double- 
bored  stopper,  into  one  hole  of  which  a  siphon  is  tightly 


Fig.  26. 

fitted.  The  siphon  should  be  fitted  with  a  rubber  tube  and 
pinchcock,  so  as  to  regulate  the  flow.  The  end  of  the  hard 
glass  tube  farthest  from  the  siphon  is  connected  with  two 
wash-bottles,  both  of  which  contain  strong  sodium  hydrox- 
ide solution.  These  wash-bottles  are  to  remove  carbon 
dioxide  from  the  air,  which  is  to  be  drawn  through  the 
tube  containing  the  copper.  When  all  connections  are 
made  air-tight,  heat  the  copper  filings  with  a  Bunsen 


256  ELEMENTS   OF  CHEMISTRY. 

burner,  and  after  a  few  minutes  start  the  aspirator  slowly. 
Air  will  now  be  drawn  into  the  apparatus  through  the 
wash-bottles  and  over  the  copper  filings.  That  which  re- 
mains will  be  collected  in  the  large  bottle.  Change  of 
color  will  occur  in  copper.  Why  ?  After  the  bottle  is 
one-half  full  of  gas,  tightly  close  the  siphon,  disconnect 
the  apparatus,  raise  the  double-bored  stopper,  and  insert 
a  burning  pine  splinter.  Note  the  difference  of  the  be- 
havior of  the  gas  as  compared  with  ordinary  air. 

Pass  a  current  of  air  over  heated  copper  filings  until  all 
original  copper  color  has  disappeared.  Connect  the  tube 
containing  this  altered  copper  with  a  hydrogen  generator, 
delivering  pure  dry  hydrogen  (Experiment  12,  Fig.  11),  and 
after  the  gas  has  passed  over  for  at  least  five  minutes,  gen- 
tly heat  the  altered  copper  by  means  of  a  Bunsen  burner. 
What  is  the  change  in  appearance.  What  collects  in  the 
farther  end  of  the  tube  ?  What  chemical  change  has  taken 
place  ? 

40.    Combustion  in  Oxygen. 

Prepare  an  'oxygen  generator  as  in  Experiment  9c.  Col- 
lect the  gas,  over  water,  in  five  wide-mouthed  32-oz.  bottles. 
Prepare  a  deflagrating-spoon  by  slipping  the  wire  handle 
through  a  hole  in  the  centre  of  a  piece  of  sheet  tin,  larger 
than  the  mouths  of  the.  bottles  (Fig.  27).  Kemove  one  of 
the  bottles  from  the  water  by  placing  a  glass  plate  over  the 
mouth,  holding  it  in  position,  and  raising  plate  and  bottle 
from  the  water.  Place  the  bottle  upright,  and  insert  a 
glowing  pine  splinter.  Into  a  second  bottle  lower  a  defla- 
grating-spoon on  which  is  a  small  piece  of  ignited  sulphur. 
Repeat  with  a  piece  of  phosphorus  the  size  of  a  pea. 
Test  the  water  remaining  in  the  jars  with  blue  litmus 
paper.  Repeat,  using  a  small  piece  of  carbon  heated  to 
redness. 

Heat  in  a  Bunsen  flame  a  4-inch  piece  of  steel  watch- 


LABORATORY  EXPERIMENTS. 


257 


spring,   and    straighten    it.       Slip    one 
end  of  the  spring  through  the  sheet-tin 
cover  used  with  the  deflagrating-spoon. 
and  fasten  with  a  cork.     Wrap  a 
bit  of  cotton  round  the  other  end, 
and   dip   it   into  a  little   molten 
sulphur.     Eemove  a  jar  of  oxy- 
gen from  the  water,  light  the  sul- 
phur,   and    when    it    is    burning 
plunge  the  watch-spring  into  the 
oxygen. 

What   is   the  difference  be- 
tween the  above  combus- 
tions and  combustions  in 
the  air  ?     Why  ? 


41.  Keversing  the  Phenomena 
of  Combustion.  Burning 
of  Oxygen  in  Hydrogen. 


Fig.  27. 


The  apparatus  necessary  to  demonstrate  the  combustion 
of  oxygen  in  hydrogen  is  shown  by  Fig.  28.    •  C  is  the  neck 
^  of  an  ordinary  retort.     Into  the  narrow 

* — ««*      end  of  this  is  fitted  a  single-bored  rub- 
ber stopper,  which  connects  at  A  with 
a  generator  furnishing  a  brisk  current  of  dry 
hydrogen,     generated    as    in    Experiment    9a. 
Allow  the  current  of  hydrogen  to  pass  for  some 
time,  until  all  air  is  expelled ;    then  light  the 
hydrogen  at  the  wide  end  of  C.     Have  ready  a 
burner,  B,  with  a  platinum  tip 
(described  in  Experiment  12), 
through  which  a  slow  stream  of 
oxygen  is  passing  from  the  gas- 
ometer.    The  oxygen  is  dried 
Fig.  28.  by  means  of  a  small  tube,  filled 


258  ELEMENTS   OF  CHEMISTRY. 

with  anhydrous  calcium  chloride.  (Wash-bottles  can- 
not be  used,  because  the  bubbling  of  the  gas  through  the 
liquid  will  cause  the  flame  to  flicker.)  Thrust  the  burner, 
through  which  oxygen  is  passing,  up  into  the  tube  C.  As 
it  passes  through  the  burning  hydrogen  at  the  mouth,  the 
oxygen  will  be  ignited,  and  will  continue  to  burn  in  C. 
What  is  the  cause  of  the  flame  ? 

42.   Heating  of  Iron  Filings  and  Sulphur.     Incandescence  during 

Union. 

Thoroughly  mix  in  a  mortar  7  grams  of  fine  iron  filings 
and  4  grams  of  flowers  of  sulphur.  Place  the  mixture  in 
a  large  test-tube,  and  hold  it  in  the  flame  so  that  it  is 
strongly  heated  at  one  point.  When  the  mass  begins  to 
glow,  remove  the  tube  from  the  flame.  What  resemblance 
is  there  between  this  change  and  those  encountered  in 
ordinary  combustion  ?  What  is  produced  ? 

43.   a.    Combustion  of  Phosphorus  in  Chlorine. 
(Experiment  under  Hood.) 

Place  a  piece  of  phosphorus  as  large  as  a  pea  in  a  defla- 
grating-spoon,  fitted  with  a  piece  of  sheet  tin  as  described 
in  Experiment  40.  Ignite  the  phosphorus,  and  lower  it 
into  a  jar  of  dry  chlorine.  Compare  this  combustion  with 
that  of  phosphorus  in  oxygen.  What  is  the  product  in 
each  case  ?  Is  there  an  evolution  of  light  and  heat  ? 

b.  Heat  changes  during  the  neutralization  of  acids  by  bases. 
Repeat  Experiment  4c,  using  in  the  beaker  10  c.c.  of 
sodium  hydroxide  solution,  containing  5  grams  of  sodium 
hydroxide  to  10  c.c.  of  water.  Gradually  add  hydrochloric 
acid  (one  part  concentrated  hydrochloric  acid  to  one  part 
of  water),  stirring  with  the  thermometer.  Note  change  in 
temperature.  Repeat,  adding  sulphuric  acid  (one  part 
sulphuric  acid  to  five  parts  of  water). 


LAB  OR  A  TOR  Y  EXPERIMENTS. 


259 


44.  Burning  of  Phosphorus  and  of  a  Candle  in  a  Closed  Air  Space, 

and  testing,  the  Air  which  remains.     Fig.  19. 

G.  Prepare  a  float  made  of  a  flat  cork,  on  which,  is  fas- 
tened a  porcelain  crucible  cover.  Place  this  cork  in  a  pneu- 
matic trough,  with  a  piece  of  phosphorus  the  size  of  a  bean 
on  the  cover,  and  light  the  phosphorus  with  a  hot  wire. 
Invert  a  be]J  jar  of  three  litres  capacity  over  the  float, 
and  slightly  raise  the  stopper  at  the  top,  so  as  to  let  out 
the  air,  which  expands  greatly  owing  to  the  heat  given  off 
by  the  burning  phosphorus.  If  this  precaution  is  omitted, 
the  air  will  be  forced  out  at  the  bottom  of  the  jar  in  large 
bubbles,  and  the  disturbance  may  tip  over  the  phosphorus 
float.  After  the  violent  combus- 
tion is  over,  insert  the  stopper  of 
the  bell  jar,  and  allow  to  cool.  To 
test  the  remaining  gas,  add  enough 
water  to  the  pneumatic  trough  to 
make  the  level  within  and  without 
the  bell  jar  alike,  and  then  intro- 
duce a  lighted  taper. 

I.  Repeat,  attaching  a  piece  of 
candle  to  a  cork  float,  lighting  the 
candle,  and  bringing  it  under  the 

bell  jar.  When  the  light  is  extinguished,  test  the  gas 
as  before.  Compare  this  with  the  action  of  air  011  copper. 
What  is  the  distinction  between  combustion  in  air  and  in 
oxygen  ?  Does  the  candle  use  up  all  of  the  oxygen  before 
it  is  extinguished  ?  What  becomes  of  the  phosphorus  ? 
Test  the  water  in  the  apparatus  with  blue  litmus. 

45.  Determination  of  the  "Volumetric  Composition  of  the  Atmosphere. 

Fig.  30. 

Take  a  long  glass  tube,  closed  at  one  end,  and  divide  it 
into  five  equal  parts  by  means  of  rubber  rings.  Invert 
this  over  a  long  cylinder  filled  with  water,  so  that  the  level 


Fig.  29. 


200 


ELEMENTS   OF  CHEMISTRY. 


without  and  within  is  at  the  first  ring,  and  then  clamp  the 
tube  in  place.  Fix  a  piece  of  phosphorus  the  size  of  a 
bean  on  a  long  copper  wire,  bend  the  wire  as  shown-  in  the 
cut,  thrust  the  phosphorus  up  into  the  tube,  and  set  the 
apparatus  aside  for  two  days.  Then  sink  the  tube  so  that 
the  level  of  the  water  without  and  within  is  the  same. 
What  is  the  ratio  between  the  volirme  of  gft,s  remaining 
and  the  volume  of  gas  originally  present  ?  By  noting  the 
height  of  the  barometer  before  and  after  the  experiment, 
^  and  then  applying  the  necessary  cor- 

rections, quite  accurate  results  can 
be  obtained,  if  a  carefully  graduated 
tube  is  substituted  for  the  crudely 
divided  one  indicated. 

The  figures  (No.  30)  show  a  tube 
such  as  is  described.     In  one  (V)  the 
phosphorus  has  just  been  thrust  into 
the  enclosed  air  space ;  in  the  other 
(a)  the  same  tube  has  been  al- 
lowed  to    stand  two  days,   and 
then  has  been  adjusted  so  that 
the  level  without  and  within  is 
the  same. 

46.  Accurate  Determination  of  the  Vol- 
umetric Composition  of  the  Atmos- 
phere by  Means  of  the  Eudiometer 
Tube.  Teacher's  Experiment. 


Fig.  30. 


In    order    to    measure    accu- 
rately  the   relative  amounts  of 

oxygen  and  nitrogen  in  the  atmosphere,  the  eudiometer  is 
employed  (Fig.  8,  Experiment  10).  The  instrument  should 
have  a  capacity  of  100  c.c.,  should  be  partially  filled  with 
mercury,  and  inverted  over  the  mercury  trough  so  that 
about  25  c.c.  of  air  will  remain  enclosed.  About  14  c.c.  of 


LABOEAT011Y  EXPERIMENTS.  261 

dry  hydrogen  are  now  run  in,  by  slanting  the  tube  and  pla- 
cing under  its  mouth  the  delivery  tube  of  a  hydrogen  ap- 
paratus which  is  generating  pure,  dry  hydrogen.  Take  all 
the  precautions  mentioned  in  Experiment  10,  and  ignite  the 
mixture  of  gases  with  an  electric  spark.  Be  sure  to  read 
accurately  the  volume  of  air  and  the  volume  of  hydrogen 
before  the  explosion,  and  also  to  measure  the  height  of  the 
column  of  mercury  at  each  step,  as  indicated  in  Experiment 
10.  After  the  explosion,  allow  it  to  stand  for  ten  minutes, 
and  then  read  the  volume  of  remaining  gas,  and  reduce  to 
standard  conditions  exactly  as  was  done  before.  Note  the 
diminution  in  volume.  The  hydrogen  will  have  united 
with  the  oxygen  to  form  water,  therefore  one-third  of  the 
diminution  in  volume  must  have  been  due  to  oxygen. 
Why  ?  What  is  the  volumetric  composition  of  the  atmos- 
phere as  given  by  the  above  experiment  ? 

47.   Determination  of  the  Dew  Point. 

Suspend  a  thermometer  over  a  beaker  of  water  so  that 
the  bulb  is  immersed  in  the  liquid.  Note  the  temperature. 
Gradually  add  small  pieces  of  ice  to  the  water,  and  stir  the 
liquid  until  a  point  is  reached  when  moisture  begins  to  col- 
lect on  the  outside  of  the  beaker.  Note  the  temperature. 

48.   Proof  that  Carbon  Dioxide  occurs  in  the  Atmosphere. 

a.  Make  a  solution  of  calcium  hydroxide  (lime-water) 
as  in  Experiment  256.     Place  this  in  a  beaker,  and  expose 
it  to  the  air  for  some  time.     What  is  observed  ?     Explain. 

b.  Arrange  an  apparatus  as  in  Experiment  39,  Fig.  26, 
substituting  an  empty  bottle  in  place  of  the  tube  contain- 
ing copper  shavings.     Fit  this  bottle  with  a  double-bored 
rubber  stopper,  so  arranged  that  air  can  be  sucked  into 
this    empty   bottle    through   two    wash-bottles    containing 
sodium  hydroxide.     When  all  connections  are  made,  open 
the  siphon,   and  draw  air  slowlv.  through  the  apparatus. 


262 


ELEMENTS   OF  CHEMISTRY 


Remove  the  empty  bottle,  pour  quickly  into  it  some  clear 
lime-water,  and  tightly  stopper.  Does  the  lime-water 
change  ?  What  alteration  was  produced  in  the  air  by 
sucking  it  through  the  caustic  soda  solution  ?  After  the 
lime-water  has  stood  for  some  time  in  the  empty  bottle, 
open  the  bottle,  introduce  into  it  a  small  piece  of  glowing 
charcoal,  and  stopper  again.  Now  observe  the  lime-water.* 
Take  a  little  clear  lime-water  in  a  test-tube,  and  blow  a 
current  of  air  through  it  by  means  of  a  glass  tube.  Wha-t 
change  do  you  observe  ? 

49.    Preparation   of  Ammonia   Gas  from  a  Solution  of  Ammonia   in 
Water.     Fig.  31.     (Experiment  under  Hood.) 

In  a  generating-flask,  a,  of  500  c.c.  capacity  place  200  c.c. 
of  strong  ammonia  water  (aqua  ammonia  fortior).  Connect 
the  delivery  tube  with  a  so-called  drying-tower,  b,  which 

is  a  cylinder  with  a  tu- 
bulated opening  below, 
and  with  a  single-bored 
stopper  and  delivery 
tube  above.  The 
drying-tower  contains 
pieces  of  quicklime. 
When  the  apparatus 
is  ready,  heat  the  gas 
gently,  and  collect  sev- 
eral cylinders  of  it  by 
upward  displacement 
of  the  air,  c.  Finally, 
collect  the  remaining 
gas  in  a  beaker  of 
water.  Cover  the  jars 
with  glass  plates  as 
fast  as  they  are  filled. 


Fig.  31. 


*  Charcoal,  in  burning,  produces  carbon  dioxide. 


LAB  OR  A  TOR  Y  EXPERIMENTS. 


263 


50.    Experiments  with  Ammonia. 

a.  Place  one  jar,  mouth  downward,  in  a  vessel  of  water. 
Is  ammonia  very  soluble  in  water  ?     Introduce  a  lighted 
splinter  into  the  second  jar.     Test  the  odor  of  ammonia  as 
you  did  that  of  chlorine.     Test  the  solution  of  ammonia 
in  water  by  means  of  a  piece  of  red  litmus  paper.     After- 
wards expose  this  litmus  paper  to  the  air  for  a  short  time. 

b.  Bring  together,  mouth  to  mouth,  a  jar  of  ammonia 
and  an  equal-sized  jar  of  oxygen.     Tightly  hold  the  two 
in  position,  and  invert  them  several  times.     Finally  apply 
a  lighted  splinter  to  the  mouth  of  each  jar. 

51.  Decomposition  of  Ammonia  by  Metals.  Fig.  32. 
Arrange  an  apparatus  for  the  preparation  of  dry  ammo- 
nia, as  in  Experiment  49.  Connect  the  delivery-tube  with 
a  tube  of  infusible  glass,  as  in  Experiment  39.  Fill  the 
bulb  of  this  tube  with  shavings  of  magnesium;  connect 
the  farther  end  with  a  safety-bottle,  and  from  the  latter 
run  a  delivery-tube  to  a  vessel  of  water.  Invert  a  test- 
tube  full  of  water  in  the  vessel,  and  have 
it  ready  for  collecting  the  gas  evolved.  When 
all  is  ready,  heat  the  ammonia  water  in  the 
generating-flask  very  gently,  so  as  to  secure  a 


Fig.  32. 


264  ELEMENTS   OF  CIIEMISTliY. 

very  slow  evolution  of  gas.  When  all  air  lias  been 
expelled  from  the  apparatus,  heat  the  bulb  containing 
magnesium  to  a  low  red  heat,  and  collect  the  evolved 
gas  in  the  inverted  test-tube.  Remove  the  test-tube, 
closing  its  mouth  with  the  thumb,  and  instantly  apply 
a  lighted  taper.  What  change  in  the  appearance  of 
the  magnesium  ?  Expel  all  ammonia  from  the  bulb- 
tube  by  means  of  a  current  of  air,  and  add  water  to 


the  contents  of  the  bulb.     What  odor  do  you  note  ? 

52.    Decomposition  of  Ammonia  by  Chlorine. 

Prepare  a  saturated  solution  of  common  salt,  invert 
over  it  a  32-oz.  bottle  filled  with  the  same  liquid,  and 
then  replace  this  liquid  by  chlorine.  Next,  cover  the 
Fig.  chlorine  bottle  with  a  glass  plate,  and  transfer  it, 
33'  mouth  downward,  to  a  vessel  containing  ammonia 
water.  Does  the  color  of  the  chlorine  disappear  ?  Does  the 
gas  diminish  in  volume  ?  When  no  further  change  takes 
place,  again  cover  the  bottle  with  a  glass  plate,  transfer, 
mouth  downward,  to  another  vessel  containing  dilute  sul- 
phuric acid  (1  part  sulphuric  acid  to  20  of  water),  and  allow 
it  to  stand  a  few  minutes.  Then  cover  again,  invert  the 
bottle,  and  introduce  a  burning  pine  splinter.  Has  the  odor 
of  the  chlorine  disappeared  ?  What  is  the  gas  remaining  ? 

53.   Determination  of  the  Volumes  of   Hydrogen  and  Nitrogen  in  a 
Known   Volume  of  Ammonia  Gas.     Fig.  33. 

Take  a  tube  one-half  metre  in  length  and  15  cm.  in 
diameter,  closed  at  one  end.  Divide  this  tube  into  three 
equal  parts  by  two  rubber  rings.  Fill  it  with  a  saturated 
solution  of  common  salt,  and  invert  it  over  a  vessel  con- 
taining the  same  liquid.  Now  expel  the  salt  solution  by 
means  of  chlorine.  When  the  tube  is  entirely  filled  with 
chlorine,  close  the  mouth  with  the  thumb,  and  transfer, 


LABORATORY  EXPERIMENTS.  265 

mouth  dowmvard,  to  a  vessel  containing  a  solution  of  am- 
monia in  water.  When  action  has  ceased  transfer  again, 
keeping  the  mouth  tightly  closed  with  the  thumb,  to  a  cyl- 
inder one-half  metre  in  depth,  which  is  filled  with  a  dilute 
solution  of  sulphuric  acid  (1  part  of  sulphuric  acid  to  20 
of  water).  Adjust  the  tube  so  that  the  level  of  the  liquid 
without  and  within  is  the  same.  At  what  point  does  it  now 
stand  ?  Test  the  gas  which  remains  as  in  Experiment  52. 
The  tube  was  divided  into  three  equal  parts,  and  filled 
with  chlorine.  When  the  chlorine  acted  on  the  ammonia 
dissolved  in  water,  it  decomposed  an  equivalent  quantity 
of  ammonia,  and  set  free  a  corresponding  amount  of 
nitrogen.  This  nitrogen  occupies  one-third  the  volume  of 
the  chlorine  used;  but  the  chlorine  has  united  with  the 
hydrogen  which  was  originally  combined  with  this  one- 
third  volume  of  nitrogen.  As  chlorine  unites  with  hydro- 
gen, volume  for  volume,  to  form  hydrogen  chloride  (see 
Experiment  20),  it  follows  that  the  three  volumes  of 
chlorine,  indicated  by  the  three  divisions  of  the  tube,  must 
have  united  with  three  volumes  of  hydrogen;  hence,  1 
volume  of  nitrogen  was  united  with  3  volumes  of  hydrogen 
in  ammonia.  The  hydrochloric  acid  which  was  formed 
was  removed  from  the  tube  by  the  ammonia  water,  and 
any  ammonia  which  may  have  entered  the  tube  has  been 
removed  by  the  dilute  sulphuric  acid,  so  that  finally 
nothing  but  pure  nitrogen  is  left. 

54.   Decomposition   of   Ammonia   by   the  Electric  Spark.     Teacher's 
Experiment. 

Fill  a  eudiometer  tube  with  clean,  dry  mercury,  and 
invert  it  in  a  mercury  trough.  Introduce  15  c.c.  of  dry 
ammonia  gas  prepared  as  in  Experiment  49.  Note  accu- 
rately :  — 

1.  Volume  of  gas. 

2.  Height  of  barometer. 


266  ELEMENTS   OF  CHEMISTRY. 

3.  Temperature. 

4.  Height  of  column  of  mercury  in  tube. 

Connect  the  two  platinum  wires  with  an  induction  coil,  and 
allow  electric  sparks  to  pass  through  the  ammonia  until  no 
further  increase  in  volume  is  observed ;  then  disconnect 
the  coil,  allow  to  stand  for  five  minutes,  and  note :  — 

1.  Volume  of  gas. 

2.  Height  of  barometer. 

3.  Temperature. 

4.  Height  of  column  of  mercury  in  tube. 

Reduce  the  gas  volume  to  standard  conditions  of  tempera- 
ture and  pressure.  What  is  the  relation  between  the  first 
volume  and  the  second  ?  Combining  what  you  learned 
in  Experiments  53  and  54,  what  volumes  of  nitrogen  and 
hydrogen  unite  to  form  ammonia  ?  What  volume  of 
ammonia  is  produced  from  these  volumes  of  hydrogen 
and  nitrogen  ?  Compare  the  results  with  the  ones  obtained 
in  determining  the  volumetric  composition  of  water  and 
of  hydrogen  chloride.  In  the  formation  of  hydrogen  chlo- 
ride, 1  volume  of  hydrogen  -f  1  volume  of  chlorine  =  2 
volumes  of  hydrogen  chloride.  In  the  formation  of  water, 
2  volumes  of  hydrogen  -j-  1  volume  of  oxygen  =  2  vol- 
umes of  water  vapor.  What  is  the  case  with  ammonia, 
as  shown  by  Experiment  54  ? 

55.  Action  of  Ammonia  on  Hydrogen  Chloride. 
A  cheap  apparatus,  which  will  demonstrate  that  equal 
volumes  of  hydrogen  chloride  and  ammonia  unite  to  pro- 
duce a  solid,  is  described  in  the  text,  page  98.  This  exper- 
iment can,  however,  be  performed  more  accurately  and 
neatly  by  using  the  apparatus  described  in  Experiment  20, 
Figs.  16  and  17.* 

*  The  glass  stopcock  must  have  a  very  large  bore,  otherwise  the  ammo- 
nium chloride  will  fill  it,  and  prevent  communication  between  the  tubes. 


LABORATORY  EXPERIMENTS.  267 

Manipulation  exactly  as  in  the  demonstration  that  hy- 
drogen chloride  is  formed  of  equal  volumes  of  hydrogen 
and  chlorine.  Through  the  three-way  stopcock  (Fig.  17) 
pass  a  current  of  dry  ammonia  (Experiment  49,  Fig.  31), 
having  turned  the  stopcock  so  that  the  gas  passes^ in 
through  one  of  the  tubes,  and  out  at  the  narrow  tip.  Allow 
the  current  to  pass  until  you  are  sure  that  all  the  air  is 
expelled  (five  to  ten  minutes).  Now  close  this  arm  with 
the  stopcock,  and  seal  the  tip  in  the  flame  of  the  Bunsen 
burner.  Next,  fill  the  second  arm  in  the  same  way  with 
dry  hydrogen  chloride  (Experiment  16,  Fig.  13),  and,  after 
sealing  the  tip,  turn  the  stopcock  so  that  the  two  tubes 
communicate.  Allow  the  apparatus  to  stand  for  twenty- 
four  hours,  and  then,  after  scratching  one  of  the  tips  with 
a  file,  dip  it  under  dry  mercury,  and  break  the  tip. 

56.    Preparation   of    Ammonium    Chloride.      The    Decomposition   of 
Ammonium  Chloride  by  Slaked  Lime. 

a.  In  a  beaker  place  25  c.c.  of  ammonia  solution.     Take 
out  a  drop,  and  place  it  on  a  strip  of  red  litmus  paper. 
Allow  the  litmus  paper  to  stand  in  the  air  for  some  min- 
utes, and  then  examine.     To  the  solution  of  ammonia  add, 
gradually,  a    solution  of   hydrochloric   acid   until    neutral 
toward  litmus.     Kow  evaporate  the  solution  to  dry  ness  in 
a  porcelain  dish  on  a  water-bath.     What  is  the  appearance 
of  the  remainder  ?     Heat  a  little  on  a  piece  of  platinum 
foil  in  the  Bunsen  burner.     What  is  the  effect  ? 

b.  In  a  porcelain  e  vapor  at  ing-dish  place  about  10  grams 
of  quicklime,  and  gradually,  a  few  drops  at  a  time,  add 
water.     Keep  on  adding  until  the  lime  is  of  the  consist- 
ency of  very  thick  paste.     Now  arrange  an  apparatus  as 
shown  in  Fig.  31,  Experiment  49  ;  place  the  slaked  lime 
in  the  generating-flask,  and  add  to  it  10    grams  of  your 
ammonium  chloride,  which  you  have  powdered  in  a  mortar. 


268  ELEMENTS   OF  CHEMISTRY. 

Connect  all  parts  of  the  apparatus,  and  heat  the  generating- 
flask  very  gently.  Collect  the  gas  which  passes  off  by  dis- 
placement of  air,  as  was  done  in  Experiment  50.  What 
gas  has  been  collected  ?  Identify  it  by  its  action  on  a 
piece  of  moist  red  litmus  paper,  and  by  its  solubility  in 
water.  Over  the  mouth  of  one  of  the  tubes  of  gas  hold  a 
glass  rod,  on  the  tip  of  which  is  a  drop  of  a  concentrated 
solution  of  hydrochloric  acid  in  water.  What  is  the 
effect  ? 

57.  Formation   of   the   Ammonium    Salts   of    Various  Acids.      The 

Decomposition  of  these  Salts  by  Bases. 

a.  In  a  beaker  place  5  c.c.  of  a  diluted  solution  of  nitric 
acid  (1  :  5),  and  then  add  ammonia  solution  until  neutral 
toward   litmus.      What    is   the   change    in    temperature  ? 
Evaporate  to  dry  ness  on  a  water-bath.     Heat  a   little  of 
the  salt  thus  produced  on  a  piece  of  platinum  foil  in  the 
Bunsen  burner.     To  some  of  the  salt  in  a  test-tube  add  a 
concentrated  solution  of   potassium   hydroxide    (one   part 
caustic  potash  to  one  of  water).     Odor  of  gas  passing  off  ? 
In  the  mouth  of  this  test-tube  suspend  a  moist  strip  of  red 
litmus  paper,  so  that  it  does  not  touch  at  the  sides.    Over  the 
mouth  of  this  test-tube  hold  a  glass  rod,  on  the  tip  of  which 
is  a  drop  of  a  concentrated  solution  of  hydrochloric  acid. 

b.  Repeat,  using  diluted   sulphuric  acid  (1  :  5)  instead 
of  nitric  acid. 

c.  Repeat  a  and  b,  using  sodium  hydroxide  instead  of 
potassium  hydroxide. 

58.  The   Determination  of   the  Volumes  of   Hydrogen  produced   by 

the  dissolving  of  Known  "Weights  of  Metals  in  Acids.  (Repeat 
Each  of  the  Following  Experiments  until  the  Two  Results  in 
Each  Case  exactly  agree.) 

a.    Arrange  an  apparatus  as  shown  in  Fig.  34.     It  con- 
sists of  a  glass  beaker,  a,   into  which  is  placed  a  small 


L  A  E  OR  A  TOE  Y  EXPERIMENTS. 


269 


Fig.  34. 


funnel,  c,  the  stem  of  which  is  cut  off.     Ac- 

curately weigh   off   about   .1    gram   of   pure 

zinc,  place  it  under  the  inverted  funnel,  and 

nearly  fill  the   beaker  with  distilled   water. 

Now  fill  a  gas-measuring  tube,  b  (which  has 

a  capacity  of  200  c.c.,  and  which  is  graduated 

in  i  c.c.),  with  diluted  hydrochloric   acid,  in- 

vert the  tube  in  the  beaker,  and  fix  it 

in  position,  so  that  its  mouth  is  over  the 

opening    of   the    funnel.       Owing  to  its 

greater  specific  gravity,  the  hydrochloric 

acid  will  descend  into  the  water,  and  will 

come  in  contact  with  the  zinc.      All  of 

the   hydrogen    which    passes    off    must 

necessarily  collect  in  the  gas-measuring 

tube.     When  all  of   the  zinc  has  disap- 

peared, tightly  close  the  tube  with  the  thumb,  and  transfer 

it  to  a  deep  cylinder  of  pure  water  ;  clamp  so  that  the  level 

without  and  within  is  the  same.     Note  temperature  and 

barometer,  and  recalculate  the  gas-volume  to  standard  con- 

ditions.     What  weight  of  hydrogen,  in  grams,  does  this 

volume  represent  ?     From  the  data  at  hand  ascertain  the 

quantity  of  zinc  which  would  be  necessary  to  liberate  one 

gram  of  hydrogen. 

b.  Repeat  a,  using  dilute  sulphuric  acid  (1  :  10)  instead 
of  hydrochloric  acid. 

c.  Repeat  a  and  Z>,  using   about  .1   gram  of  pure  iron 
(piano  wire). 

d.  If  desired,  a  and  b  can  be  repeated,  using  a  piece 
of   magnesium  ribbon  which  has  been  carefully  cleaned. 
In  this  case  a  gas-measuring  vessel  of  at  least  300  cubic 
centimetres    capacity   must   be   selected.       What    are   the 
equivalent  weights  of  iron  and  zinc  as  slipway  by.  the  exper- 

iments?        ' 


270  ELEMENTS   OF  CHEMISTRY. 

59.    Alteration  in  "Wood  by  Heating. 

In  a  test-tube  of  so-called  infusible  glass,  place  a  piece  of 
fresh  pine  wood,  and  bring  it  into  the  flame  of  the  Bunsen 
burner.  Gradually  increase  the  heat.  Alteration  in  the 
appearance  of  the  wood  ?  Odor  ?  Apply  a  lighted  taper 
to  the  mouth  of  the  tube. 

60.    a.    The  Absorption  of  Coloring  Matter  by  Charcoal. 

1.  In  a  test-tube  place  a  little  indigo,  add  to  this  a  few 
drops  of  concentrated  sulphuric  acid,  warm  slightly,  and 
then  dilute  with  water,  and  filter.     Pour  the  blue  solution 
into  a  300  c.c.  flask  in  which  you  have  placed  10  grams  of 
fresh  animal  charcoal.*      Warm  the  solution,  and  shake 
vigorously  for  a  short  time;  then  filter  off  the  charcoal. 
What  is  the  color  of  the  filtrate  ? 

2.  Repeat,  using  a  solution  of  blue  litmus. 

3.  Repeat,  using  a  solution  of  logwood. 

b.    Absorption  of  gases  by  charcoal. 

Arrange  an  apparatus  for  the  preparation  of  ammonia  as 
in  Experiment  49,  Fig.  31.  Collect  a  test-tube  full  of  the 
gas  over  dry  mercury,  and  leave  the  test-tube  clamped  in 
position,  so  that  its  mouth  dips  under  the  mercury.  Now 
heat  a  small  piece  of  wood-charcoal  for  an  instant  in  the 
flame  of  the  Bunsen  burner,  f  After  allowing  any  portion 
which  may  be  glowing  to  become  extinguished,  slip  it 
quickly  under  the  mercury,  so  that  it  will  rise  in  the  test- 
tube.  When  no  further  absorption  takes  place,  prepare  a 
second,  piece  of  charcoal  as  above,  and  bring  it  into  the 
tube.  What  is  true  of  ammonia  gas  is  true  of  a  large 
number  of  other  gases  which,  like  ammonia,  are  easily 
condensed  to  liquids  (sulphur  dioxide,  hydrogen  sulphide, 
etc.). 

*  Animal  charcoal  is  to  be  obtained  from  any  dealer  in  chemicals. 
t  Hold  the  charcoal  by  a  pair  of  pincers  or  a  pair  of  tongs. 


LABORATORY  EXPERIMENTS. 


271 


61.    Burning  of  Charcoal  in  a  Closed  Space  of  Oxygen. 

Prepare  a  glass  tube  30  cm.  in  length  and  10  cm.  inter- 
nal diameter,  sealed  at  one  end,  and  bent  as  shown  in 
Fig.  35.  Slip  into  the  tube  a  piece  of  wood-charcoal  the 
size  of  a  pea,  fill  the  tube  with  mercury,  and  invert  it  in  a 
small  vessel,  b,  of  the  same  liquid, 
clamping  it  in  position  as  shown  in 
the  cut.  Now  admit  dry  oxy- 
gen into  the  tube  until  the  mer- 
cury is  expelled  as  far  as 
the  bend,  and  mark  the 
position  of  the  liquid  by 
means  of  a  strip  of 
paper.  Now  gently 
heat  the  charcoal  with 
the  Bunsen  burner  un- 
til combustion  begins, 
then  remove  the  flame, 
and  allow  the  charcoal  to  stand  until  combustion  is  complete, 
and  the  apparatus  has  cooled  to  its  former  temperature.  Is 
there  any  change  in  the  volume  of  the  gas  ? 


Fig.  35. 


62.   Formation  of  Carbon  Dioxide  by  passing  Oxygen  over  Hot 
Charcoal. 

Arrange  the  apparatus  used  in  Experiment  21,  Fig.  18, 
with  the  difference  that  in  place  of  the  hydrochloric  acid 
generator  (A),  you  have  an  apparatus  delivering  dry  oxygen. 
Fill  the  iron  tube  with  about  15  grams  of  charcoal  in 
pieces  the  size  of  a  pea,  connect  all  parts  of  the  apparatus, 
and  collect  the  gas  which  passes  off  by  displacement  of  air 
in  several  cylinders  placed  mouth  upward.  Cover  each 
cylinder,  after  the  air  is  expelled,  with  a  glass  plate.  Into 
one  of  the  cylinders  introduce  a  burning  taper.  iDto  an- 
other pour  a  few  drops  of  a  filtered  solution  of  slaked  lime 


272 


ELEMENTS   OF  CHEMISTRY. 


[Experiment  25&]  (formation  of  calcium  carbonate).  In- 
vert a  cylinder  in  a  vessel  containing  a  solution  of  caustic 
potash.  In  one  of  caustic  soda. 


63.    Formation  of  the  Primary  and  Secondary  Carbonates  of  Potas- 
sium and  Sodium. 

For  these  experiments,  arrange  an  apparatus  for  generat- 
ing carbon  dioxide  as  described  in  Experiment  65. 

a.  Prepare  a  solution  of  10  grams  of  potassium  hydrox- 
ide in  50   grams  of  water,  place  this  solution  in  a  small 
beaker,  attach  a  funnel  small  enough  to  pass  inside  this 
beaker  to  the  exit  tube  of  an  apparatus  generating  carbon 
dioxide,  and  then  dip  the  funnel  into  the  beaker  so  that  its 
edge  is  just  below  the   surface  of  the   liquid  (Fig.  36). 
Now  pass  a  brisk  current  of  carbon  dioxide  into  the  solu- 
tion of  caustic  potash  until  a  drop,  taken  out  and  placed 
on  a  piece  of  red  litmus  paper,  is  neutral.     Now  evapo- 
rate gently  to  dryness  in  a  porcelain  dish  on  a  water-bath. 

What  is  the  appearance  of  the 
'*—  remainder?  Is  it  like  caustic 

potash  ?  Place  a  little  of  the  re- 
mainder in  a  test-tube,  and  add  to  it  a 
few  drops  of  diluted  hydrochloric  acid, 
and  then  in  the  mouth  of  the  tube  hold 
a  glass  rod,  on  the  tip  of  which  you 
have  a  drop  of  clear  solution  of  slaked 
lime.  Compare  this  behavior  with  that 
of  caustic  potash  under  the  same  con- 
ditions. Heat  some  of  the  remainder 
in  a  test-tube,  and  hold  over  the  mouth 
a  glass  rod,  on  the  tip  of  which  is  a 
drop  of  a  clear  solution  of  slaked  lime. 

b.  Purify  5   grams  of  the  primary  carbonate  of  potas- 
ium  (prepared  by  the  above  experiment),  by  dissolving  it 


Fig.  36. 


LABORATORY  EXPERIMENTS.  273 

in  cold  distilled  water,  evaporating  the  solution  at  a  gentle 
heat  to  crystallization,  and  then  drying  the  crystals  between 
pieces  of  filter  paper.  Finally,  powder  the  crystals,  and 
place  them  in  a  desiccator  over  concentrated  sulphuric  acid 
for  twenty-four  hours.  Take  a  gas-measuring  tube  (of  100 
c.c.  capacity,  and  graduated  to  .1  c.c.),  fill  it  with  dry 
mercury,  and  invert  it  over  a  trough  of  the  same  liquid. 
Now  carefully  weigh  off  .2  grams  of  your  pure  primary 
carbonate  of  potassium,  wrap  it  in  a  piece  of  filter  paper 
so  as  to  form  a  package  small  enough  to  slip  up  into  the 
mercury  tube,  and  then  bring  it  under  the  mouth  so  that 
it  will  rise  to  the  top.  From  a  curved  pipette  (Fig.  24) 
introduce  a  few  drops  of  diluted  hydrochloric  acid  into  the 
tube.  What  is  the  effect  ?  When  the  gas  no  longer  in- 
creases in  volume,  introduce  another  drop  of  the  acid,  and 
see  if  it  has  any  further  effect.  Carefully  continue  this 
operation  until  no  further  evolution  of  gas  and  increase  in 
volume  are  observed.  Now  allow  the  tube  to  stand  for  some 
minutes,  and  then  measure  the  gas  volume,  taking  account 
of  the  temperature,  barometer,  and  height  of  the  column 
of  mercury  in  the  gas-measuring  tube.  Reduce  the  gas 
volume  to  standard  conditions  of  temperature  and  pressure. 
What  weight  of  carbon  dioxide  is  liberated  by  one  gram 
of  potassium  primary  carbonate  ?  * 

c.  Carefully  weigh  off  2  grams  of  pure,  dry  primary 
carbonate  of  potassium,  and  place  it  in  a  deep  porcelain 
crucible  or  test-tube  of  infusible  glass.  Weigh  the  whole, 
and  then  heat,  gently  at  first,  and  finally  to  a  red  heat 
for  fifteen  minutes.  Allow  it  to  cool,  and  again  weigh. 
What  is  the  loss  in  weight  ?  What  is  the  weight  of  the 
remainder  ?  Continue  the  above  operation  until  no  fur- 
ther change  in  weight  takes  place.  What  volume  of  carbon 
dioxide  would  this  loss  i-n  weight  represent  ?  Compare 

*  One  cubic  centimetre  of  carbon  dioxide  weighs  .001986  gram. 


274  ELEMENTS   OF  CHEMISTRY. 

this  volume  with  that  given  off  by  2  grams  of  primary 
potassium  carbonate  when  treated  with  acids  (&).  Weigh 
carefully  .138  gram  of  pure,  dry  secondary  potassium  car- 
bonate, and  with  this  repeat  b.  Compare  the  volume  of 
carbon  dioxide  given  off  with  that  formed  in  b.  From  the 
data  thus  obtained,  calculate  the  weight  of  primary  potas- 
sium carbonate  which  would  contain  one  molecular  weight 
of  carbon  dioxide.  Calculate  the  amount  of  potassium 
hydroxide  combined  with  one  molecular  weight  of  carbon 
dioxide. 

64.  Prepare  a  solution  of  potassium  hydroxide  as  indi- 
cated in  Experiment  27 'a.  Now  weigh  off  1  gram  of  pri- 
mary potassium  carbonate,  dissolve  in  25  c.c.  of  water,  place 
in  a  beaker,  and  carefully  add  to  it  from  the  burette  an 
amount  of  potassium  hydroxide  solution  representing  .56 
gram  of  solid  potassium  hydroxide.  Evaporate  the  solu- 
tion so  formed  to  dryness,  and  heat  a  little  of  the  remainder 
in  a  test-tube.  Does  it  give  off  carbon  dioxide  ?  To  a 
little  in  a  test-tube  add  a  few  drops  of  a  dilute  solution  of 
hydrochloric  acid.  Hold  a  glass  rod,  on  the  tip  of  which 
is  a  drop  of  a  clear  solution  of  slaked  lime,  over  the  mouth 
of  the  tube,  after  adding  acid.  Is  the  product  of  the 
action  of  potassium  hydroxide  on  primary  potassium  car- 
bonate primary  or  secondary  potassium  carbonate  ? 

65.    Preparation  of  Carbon  Dioxide  for  Laboratory  Use. 

The  apparatus  is  the  same  as  that  represented  by 
Fig.  13. 

In  the  generating-flask  place  about  25  grams  of  clean 
marble  *  in  pieces  the*  size  of  a  hickory-nut.  Connect  all 
parts  of  the  apparatus  (have  some  pure  water  in  the  wash- 
ing-bottle), and  then  pour  diluted  hydrochloric  acid  (one 

*  Completely  fill  the  flask  with  water  before  dropping  in  the  pieces 
of  marble,  and  after  all  is  added  pour  off  the  water.  If  this  precaution 
is  not  taken,  the  pieces  of  marble  may  crack  the  flask  as  they  are  dropped. 


LABORATORY  EXPERIMENTS.  275 

part  concentrated  acid  to  five  of  water)  in  through  the 
safety  tube.  Collect  the  gas  which  is  evolved  in  a  cylin- 
der, which  is  placed  mouth  upward.  Place  a  burning 
candle  in  a  cylinder  of  air,  and  then  pour  into  it  carbon 
dioxide  from  a  second  cylinder,  just  as  one  would  pour 
water.  Into  a  cylinder  of  carbon  dioxide  place  a  little 
blue  litmus  solution,  cover  the  cylinder  with  a  glass  plate, 
and  shake.  Invert  a  test-tube  full  of  carbon  dioxide  over 
a  solution  of  potassium  hydroxide. 

66.  Formation  of  the  Secondary  and  Primary  Carbonates  of  Calcium. 
In  a  beaker  place  15  c.c.  of  a  clear  solution  of  slaked 
lime.  Into  this  solution  pass  carbon  dioxide  from  the 
generator.  Continue  to  pass  in  carbon  dioxide  until  the 
white  precipitate,  which  is  at  first  produced,  disappears. 
When  the  solution  is  clear,  discontinue  the  carbon  dioxide, 
and  then  warm  the  water  in  the  beaker  to  boiling. 

67.   Preparation  of  Carbon  Monoxide. 

Arrange  a  carbon  dioxide  apparatus  as  in  Experiment  66. 
Connect  the  delivery  tube  with  an  iron  tube  which  you  can 
heat  in  a  furnace,  as  in  Experiment  21,  Fig.  18.  Introduce 
a  safety-bottle,  c,  after  the  iron  tube;  put  in  the  tube  15 
grams  of  charcoal  in  pieces  the  size  of  a  pea,  connect  all 
parts  of  the  apparatus,  heat  the  iron  tube  to  redness,  and 
then  pass  a  slow  current  of  carbon  dioxide  over  the  char- 
coal. Collect  the  evolved  gas  in  cylinder  over  a  dilute 
solution  of  potassium  hydroxide  (1 :  20).  When  the  quan- 
tity is  sufficient,  remove  one  of  the  cylinders,  place  it 
mouth  upward,  and  introduce  a  lighted  taper.  After  com- 
bustion is  over,  pour  a  little  of  a  clear  solution  of  slaked 
lime  into  the  cylinder,  cover  with  a  glass  plate,  and  shake. 
Is  the  gas  which  you  have  obtained  by  the  action  of  carbon 
dioxide  on  charcoal  soluble  in  potassium  hydroxide  ?  How 
does  it  differ  from  carbon  dioxide  ? 


276 


ELEMENTS   OF  CHEMISTRY. 


68.  Preparation  of  Methane.  (Hydrogen  Carbide.) 
The  apparatus  is  shown  by  Fig.  37.  The  tube  a  is  of 
so-called  infusible  glass,  sealed  at  one  end,  and  stoppered 
with  a  single-bored  rubber  stopper,  which  is  connected 
with  a  safety  bottle  and  delivery  tube.  Prepare  an  inti- 
mate mixture  in  a  mortar,  of  10  grams  of  sodium  acetate 
(which  has  previously  been  dried  by  heating  to  fusion  in 
an  open  dish),  and  10  grams  of  a  mixture  of  sodium  hydrox- 


Fig.  37. 


ide  and  calcium  oxide  (so-called  soda-lime),*  and  then  half 
fill  your  tube  with  this  mixture.  Place  the  tube  on  its 
side,  and  pound  it  lightly  on  the  table  until  you  have 
formed  a  canal  for  the  free  passage  of  the  gas.f  Now 
connect  all  parts  of  the  apparatus,  and  wrap  a  piece  of 
wire  gauze  around  the  tube,  to  prevent  its  cracking  when 

*  Soda-lime  can  be  purchased  of  dealers  in  chemicals. 

t  One  must  be  absolutely  certain  that  there  is  no  packing  of  the  mix- 
ture in  the  tube.  Any  portion  of  the  tube  which  may  be  closed  gas-tight 
will  cause  a  dangerous  explosion,  by  preventing  the  escape  of  gas. 


LABORATORY  EXPERIMENTS.  277 

heated.  Then  heat  gently  with  a  Bunsen  burner,  begin- 
ning at  the  closed  portion  of  the  tube,  until  there  is  a  regu- 
lar evolution  of  gas.  Wait  until  all  air  is  expelled  from 
the  apparatus,  and  then  collect  in  cylinders  or  test-tubes, 
over  water. 

69.   Properties  of  Methane 

Remove  one  of  the  cylinders  from  the  water,  invert  it, 
and  instantly  apply  a  lighted  taper  to  the  mouth.  Remove 
a  second  cylinder,  place  it  mouth  upward,  allow  it  to  stand 
for  a  few  seconds,  and  then  apply  a  lighted  taper.  What 
is  the  effect  ?  Is  methane  specifically  heavier  or  lighter 
than  air  ?  Remove  a  third  cylinder,  light  the  gas  while 
it  is  held  mouth  downward ;  now  invert  the  cylinder. 
Into  a  cylinder  in  which  you  have  burned  methane  pour 
a  few  drops  of  a  clear  solution  of  slaked  lime,  cover  the 
cylinder  with  a  glass  plate,  and  shake. 

70.  The  Volumetric  Composition  of  Methane.  Teacher's  Experiment. 
The  apparatus  is  given  by  Fig.  9,  Experiment  11.  Fill 
the  graduated  eudiometer  tube  with  clean,  dry  mercury, 
and  invert  it  in  the  deep  cylinder  as  described  in  Experi- 
ment 11.  Now  introduce  about  10  to  15  c.c.  of  pure,  dry 
methane  (prepared  as  in  Experiment  68)  into  the  tube, 
pass  steam,  into  the  jacket  until  the  temperature  is  con- 
stant, and  then  carefully  measure  the  gas-volume  after 
taking  the  usual  observations.  (What  are  they  ?)  Now 
pass  in  approximately  25  c.c.  of  dry  oxygen,  allow  to 
remain  for  a  minute,  and  again  measure.  Then  lower  the 
tube  into  the  mercury  cylinder  as  far  as  it  will  go,  wrap 
a  towel  around  the  mouth  of  the  cylinder,  so  as  to  prevent 
spattering,  and  explode  with  a  spark  from  an  induction 
coil  (Experiment  10).*  Bring  the  eudiometer  tube  back 

*  Be  sure  that  the  steam-jacket  is  thoroughly  heated  during  the 
entire  experiment. 


278  ELEMENTS   OF  CHEMISTRY. 

into  position,  so  that  the  height  of  the  column  of  mercury 
is  the  same  as  it  was  before  the  explosion,  and  note  if 
there  was  any  change  in  the  volume  of  gas.  Now  allow 
to  cool  until  the  entire  apparatus  is  at  the  temperature  of 
the  surrounding  air;  then  introduce  a  drop  of  water  into 
the  eudiometer,*  and  measure  the  volume  as  before,  this 
time  taking  the  tension  of  water  vapor  into  account  during 
your  calculations.  Next,  cut  a  small  piece  of  potassium 
hydroxide,  take  it  by  a  pair  of  pincers,  and  slip  it  under 
the  eudiometer  tube,  so  that  it  will  rise  to  the  upper  level 
of  the  mercury.  Allow  to  stand  until  no  further  contrac- 
tion in  volume  takes  place,  and  then  again  measure  the 
gas-volume.  (This  time  neglect  the  pressure  of  water 
vapor.)  The  volume  of  contraction  on  cooling  corresponds 
to  the  volume  of  what  product  of  the  explosion  ?  The 
volume  of  contraction  after  adding  potassium  hydroxide  ? 
From  the  data  you  have  obtained,  calculate  the  composi- 
tion of  methane  by  volume. 

71.    The  Action  of  Chlorine  on  Methane. 

Take  two  jars  of  the  same  size,  with  ground  tops ;  fill 
one  with  chlorine  (Experiment  21&),  and  the  other  with 
methane  over  water  (Experiment  68).  Cover  each  jar  with 
a  glass  plate,  bring  them  together,  mouth  to  mouth,  then 
remove  the  plates  which  separate  them,  hold  "tightly  in 
position,  and  invert  several  times.  When  the  gases  have 
completely  mixed,  apply  a  lighted  taper  to  the  mouth  of 
each.  Result  ? 

72.   The  Gradual  Action  of  Chlorine  on  Methane. 

a.  The  apparatus  is  that  described  in  Experiment  20, 
Figs.  16  and  17,  and  the  manipulation  is  the  same,  except- 

*  This  drop  of  water  is  introduced  so  as  to  be  certain  that  the  gases 
to  be  measured  are  completely  saturated  with  moisture. 


LABORATORY  EXPERIMENTS.  279 

ing  that  one  of  the  arms  of  the  double  tube  is  filled  with 
methane  instead  of  hydrogen.  The  apparatus  must  stand 
for  at  least  twenty-four  hours  in  daylight  or  sunlight  before 
the  reaction  is  completed  and  the  color  of  chlorine  has 
entirely  disappeared.  After  this  time  bring  one  of  the 
arms  of  the  tube  into  a  solution  of  blue  litmus,  and,  after 
scratching  with  a  file,  break  the  tip.  Change  in  the  color 
of  litmus  ?  What  portion  of  the  apparatus  becomes  filled 
with  the  litmus  solution  ?  After  allowing  to  stand  for 
a  few  minutes,  remove  the  tube  from  the  liquid,  turn  the 
stopcock  so  that  this  fluid  can  drain  off,  then  bring  the 
opened  end  of  the  tube  into  a  deep  cylinder  of  mercury 
(described  in  Experiment  11,  Fig.  9),  and  press  down  until 
the  liquid  rises  to  the  stopcock.  Turn  the  stopcock  as 
it  was  before,  and  then  break  off  the  second  tube  which 
extends  upward,  quickly  apply  a  lighted  taper  to  its  mouth, 
and  force  out  the  remaining  gas  by  pressing  the  apparatus 
down  into  the  mercury.  Color  of  flame  ?  To  the  solution 
of  blue  litmus  add  a  few  drops  of  a  solution  of  silver 
nitrate.  Result  ?  What  insoluble  substance  separates  ? 

73.    The  Action  of  Chlorine  on  Methyl  Chloride. 

Repeat  Experiment  72,  with  the  difference  that  after 
you  have  opened  the  tube  under  litmus  solution  you  allow 
the  liquid  to  drain  off,  and  then,  after  drying,  once  more 
fill  it  with  chlorine,  and  seal  the  tip,  while  the  branch  con- 
taining methyl  chloride  is  carefully  kept  closed.  After 
establishing  communication  between  the  two  arms  of  the 
tube,  allow  to  stand  in  the  daylight,  and  then  follow 
directions  as  in  Experiment  72.  Compare  the  two  results. 

74.    The  Action  of  Chlorine  on  Methylene  Chloride. 

Repeat  Experiment  73,  using  the  apparatus  in  which 
you  have  produced  methylene  chloride ;  i.e.,  which  contains 


280  ELEMENTS  OF  CHEMISTRY. 

methane  which  has  twice  been  acted  on  by  chlorine.  After 
the  chlorine  has  acted  on  the  methylene  chloride  for  twenty- 
four  hours,  open  the  tube,  as  before,  under  a  solution  of  lit- 
mus, and  note  the  result.  How  does  this  differ  from  the 
two  preceding  cases  ?  Odor  of  product  which  is  formed  ? 

75.    The  Formation  of  Salts  by  Double  Decomposition. 

a.  To  a  solution  of  barium  chloride  in  a  test-tube  add 
a  few  drops  of  a  diluted  solution  of  sulphuric  acid.  What 
is  formed  ?  Does  the  precipitate  dissolve  on  boiling  ? 
Does  it  dissolve  in  an  excess  of  sulphuric  acid? 

I).  Repeat  a,  using  a  solution  of  potassium  sulphate 
instead  of  one  of  sulphuric  acid. 

c.    Repeat  b,  using  a  solution  of  magnesium  sulphate. 

76.    Precipitation  of  Salts  by  Double  Decomposition. 

a.  To  a  solution  of  calcium  chloride  add  a  few  drops  of  a 
solution  of  potassium  carbonate.     What  is  formed  ?     Does 
the  precipitate  dissolve  on  boiling  ?     Filter  the  precipitate 
after  boiling,  and  to  the  substance  on  the  filter  paper  add 
a  few  drops  of   hydrochloric  acid.     Does   the  precipitate 
dissolve  ?    See  if  the  precipitate  will  dissolve  in  nitric  acid. 
In  sulphuric  acid.     What  gas  passes  off  in  each  case  ? 

b.  Repeat  «,  using  a  solution  of  barium  chloride  instead 
of  one  of  calcium  chloride. 

c.  To  a  solution  of  sodium  chloride  add  a  few  drops  of 
a  solution  of  silver  nitrate.     What  is  formed  ?     Does  the 
precipitate  dissolve  on  boiling  ?    Does  it  dissolve  in  hydro- 
chloric acid  ?     In  nitric  acid  ?     To  the  precipitate  add  a 
slight  excess  of  a  solution  of  ammonia  in  water.     Does  it 
dissolve  ? 

d.  Repeat  c,  using  solution  of  hydrochloric  acid  instead 
of  sodium  chloride. 

e.  To  a  solution  of  magnesium  sulphate  add  a  few  drops 


LABORATORY  EXPERIMENTS.  281 

of  a  solution  of  barium  chloride,  and  repeat  directions  in 
Experiment  75a.  Compare  the  result  with  that  obtained 
in  75a. 

77.  The  Action  of  Chlorine  on  Hydrobromic  Acid,  Hydriodic  Acid, 

Sodium  Bromide,  and  Sodium  Iodide. 

a.  Obtain  a  solution  of  hydrobromic  acid  from  the  side- 
table,  place  a  little  in  a  test-tube,  add  to  it  three  or  four 
drops  of   carbon    bisulphide,  and  then   add  a   little  of   a 
solution  of   chlorine    in  water.     Close    the    mouth  of   the 
tube  with  the  thumb,  and  shake.     Change  of  color  in  the 
carbon  bisulphide  ?  *     What  change  takes  place  ? 

b.  Repeat  a,  using  a  solution  of  hydriodic  acid.     (Take 
care  not  to  add  more  than  a  little  chlorine  water,  other- 
wise the  color  of  the  separated  iodine  may  be  destroyed.) 
Color  of  a  solution  of  iodine  in  carbon  bisulphide  ? 

c.  Repeat  b,  using  a  solution  of  bromine  in  water  instead 
of  one  of  cholorine. 

d.  Repeat  a,  b,  and  c,  using  solutions  of  potassium  bro- 
mide and  iodide  instead  of  hydrobromic   acid  and  hydro- 
iodic  acid. 

78.  The  Preparation  of  Hydrogen  Sulphide.     (All  Experiments  with 

Hydrogen  Sulphide  must  be  performed  under  the  Hood.) 

The  apparatus  is  the  same  as  that  used  for  the  prepara- 
tion of  hydrogen  chloride  (Experiment  16,  Fig.  13).  Into 
the  gas-generating  flask  place  10  grams  of  fused  ferrous 
sulphide  (precautions  in  this  case  as  in  Experiment  65) 
about  the  size  of  a  bean,  connect  all  parts  of  the  apparatus, 
and  add  diluted  sulphuric  acid  (1  : 5)  through  the  safety 
tube.  The  wash-bottle  should  contain  pure  water.  Collect 

*  Carbon  bisulphide  dissolves  bromine  and  iodine  so  readily  that  it 
will  extract  them  from  their  solutions  in  water.  Their  color  is  there- 
fore rendered  more  apparent  by  being  concentrated  in  the  fow  drops  of 
carbon  bisulphide. 


282  ELEMENTS   OF  CHEMISTRY. 

the  gas  in  jars  by  displacement  of  air,  taking  care  during 
the  operation  to  partly  cover  each  jar  with  a  glass  plate,  so 
as  to  just  leave  room  for  the  delivery-tube  of  the  apparatus. 
Completely  cover  the  jars  with  glass  plates  as  fast  as  they 
are  filled.  Remove  the  cover  of  one  of  the  jars,  and  apply 
a  lighted  taper.  What  separates  on  the  sides  of  the  jar  ? 
Why  ?  Is  the  result  different  if  you  mix  hydrogen  sul- 
phide with  oxygen,  and  then  ignite  ?  (Perform  this  latter 
experiment  in  a  test-tube,  and  wrap  a  towel  around  it 
before  approaching  the  flame.)  Odor  of  hydrogen  sul- 
phide? (Precautions  as  in  testing  the  odor  of  chlorine.) 
Solubility  of  hydrogen  sulphide  in  water  ? 

79.   The  Action  of  Hydrogen  Sulphide  on  the  Salts  of  Metals.     For- 
mation of  Sulphides  which  do  not  dissolve  in  Dilute  Acids.* 

a.  In  a  test-tube  prepare  a  solution  of  copper  sulphate 
in  water,  add  two  or  three  drops  of  hydrochloric  acid,  and 
then  pass  hydrogen  sulphide  into  the  solution.     Color  of 
precipitate  ?     Filter  the  precipitate,  wash  it  with  warm 
water,  dry  it  011  its  filter,  and  then  bring  it  into  a  second 
test-tube.     Is   it   soluble  in  cold  hydrochloric  acid  ?     In 
hot  hydrochloric  acid  ?     In  nitric  acid  ?     In  a  mixture  of 
one  part  nitric  acid  to  three  parts  hydrochloric  acid  ? 

b.  Repeat  a,  substituting  a  solution  of  lead  acetate  for 
copper  sulphate,  and  in  this  case  acidify  with  two  drops 
of  nitric  acid  instead  of  hydrochloric  acid. 

c.  Repeat  a,  using  a  solution  of  the  oxide  of  arsenic  in 
an  excess  of  hydrochloric  acid. 

d.  Repeat  a,  using  a  solution  of  silver  nitrate,  acidified 
with  a  few  drops  of  nitric  acid. 

*  In  working  with  hydrogen  sulphide,  pass  the  gas  into  the  solutions 
through  a  tuhe  with  a  very  small  bore  (a  so-called  capillary  tube).  By 
this  means  excessive  waste  of  the  gas  by  reason  of  a  too  rapid  cur- 
rent is  avoided,  and  the  danger  of  poisonous  effects  is  reduced  to  a 
minimum. 


LABORATORY  EXPERIMENTS.  283 

80.   Formation  of  Sulphides  which  dissolve  in  Dilute  Acids. 

a.  Repeat  79a,  using  a  solution  of  zinc  sulphate  which 
you  have  not  acidified.     Filter  whatever  precipitate  you 
may  have,  and  test  the  clear  filtrate  with  a  strip  of  blue 
litmus  paper.     Is  it  acid  ?     To  the  clear  filtrate  add  a  few 
drops  of  a  solution  of  potassium    sulphide.*     Does  zinc 
sulphide    separate    from  this    filtrate  ?     To  zinc  sulphide 
add  a  few  drops  of  hydrochloric  acid.     Odor  of  gas  pass- 
ing  off   on   acidifying?     Compare    the    result   with   that 
obtained  by  adding  hydrochloric  acid  to  calcium  carbonate 
(Experiment  76). 

To  a  solution  of  zinc  sulphate  which  has  been  acidified 
with  a  few  drops  of  sulphuric  acid  add  hydrogen  sulphide. 
Is  there  any  precipitate  ?  To  this  solution  add  potassium 
sulphide.  Result  ? 

b.  Repeat  a,  using  a  solution  of  ferrous  sulphate  (green 
vitriol). 

81.   The  Separation  of  Two  Metals  by  using  Hydrogen  Sulphide. 

In  a  test-tube  place  a  little  of  a  solution  of  zinc  sulphate, 
and  add  to  it  the  same  quantity  of  a  solution  of  copper 
sulphate.  Acidify  with  three  or  four  drops  of  dilute 
sulphuric  acid,  and  then  pass  in  hydrogen  sulphide.  Con- 
tinue to  pass  in  the  gas  until  its  odor  remains  in  the  solu- 
tion after  standing  for  some  time.  Now  filter  off  the 
copper  sulphide  which  is  formed,  and  to  the  filtrate  add 
a  solution  of  potassium  sulphide.  Result  ? 

*  In  order  to  prepare  potassium  sulphide,  dissolve  5  grams  of  potas- 
sium hydroxide  in  50  c.c.  of  water,  take  one-half  of  the  solution,  and 
pass  in  hydrogen  sulphide  until  no  more  gas  will  dissolve.  Now  pour 
into  this  the  other  half  of  the  solution. 


284 


ELEMENTS   OF  CHEMISTRY. 


The  Principal  Elements,  with  Their  Atomic  "Weights. 


NAME  OF 
ELEMENT. 

CHEMICAL 
SYMBOL. 

USUAL  CONDITION. 

ATOMIC 
WEIGHT. 

SPECIFIC 

GRAVITY. 

Aluminium 

Al. 

White,  metallic  solid 

27. 

2.56 

Antimony 

Sb. 

Crystalline,  metallic  solid 

120. 

6.7 

Arsenic 

As. 

Gray,  crystalline  solid 

75. 

5.7 

Barium 

Ba. 

Reddish  metal,  attacked  by  water 

137.5 

3.7 

Bismuth 

Bi. 

Reddish  crystalline  metal 

208.9 

9.7 

Boron 

B. 

Grayish-black  powder 

11. 

2.68 

Bromine 

Br. 

Dark  brown  liquid 

80. 

3.2* 

Calcium 

Ca. 

Reddish  metal.    Attacks  water 

40. 

1.57 

Carbon 

C. 

Solid,  appears  in  3  forms  :  dia- 

mond, graphite,  and  charcoal 

12. 

2.2 

Chlorine 

Cl. 

Greenish-yellow  gas 

35.5 

2.45  f 

Chromium 

Cr. 

Grayish  metallic  powder 

52.1 

6.8 

Copper 

Cu. 

Red  metal 

63.6 

8.8 

Gold 

Au. 

Yellow  metal 

197.3 

19.3 

»  Hydrogen 

H. 

Colorless  gas 

1. 

.069  1 

Iodine 

I. 

Black,  crystalline  solid 

127. 

4.95 

Iron 

Fe. 

Grayish  metal 

56. 

7.8 

Lead 

Pb. 

Gray,  soft  metal 

207. 

11.44 

Magnesium 

Mg. 

White  metal 

24.3 

1.74 

Manganese 

Mn. 

Grayish-white  metal 

55. 

8. 

Mercury 

Hg. 

White,  liquid  metal 

200. 

13.6 

•    Nitrogen 

N. 

Colorless  gas 

14. 

.972  1 

\  Oxygen 

0. 

Colorless  gas 

16. 

1.105  f 

Phosphorus 

P. 

In  2  forms  :  a  yellow  solid  and  a 
red  powder 

31. 

1.83  to  2.1 

Potassium 

K. 

Grayish  metallic  solid.    Attacks 

water 

39. 

.865 

Silicon 

Si. 

Black  solid   in  small,  lustrous 

crystals 

28.4 

2.5 

Silver 

Ag. 

White,  metallic  solid 

108. 

10.5 

Sodium 

Na. 

White,  metallic  solid.    Attacks 

23. 

.972 

water 

Sulphur 

S. 

Yellow  solid 

32. 

2.045 

Tin 

Sn. 

White  metal 

119. 

7.3 

Zinc 

Zn. 

Grayish-white  metal 

65.3 

7.15 

*  Specific  gravity  as  liquids. 

t  Specific  gravity  as  gases  ;  air  =  1. 


SCIENCE.    *  51 


Descriptive  Inorganic  General  Chemistry 

A  text-book  for  colleges,  by  Professor  PAUL  C.  FREER,  University  of 
Michigan.     Revised  Edition.     8vo,  cloth,  559  pages.     Price,  $3.00. 

IT  aims  to  give  a  systematic  course  of  Chemistry  by  stating 
certain  initial  principles,  and  connecting  logically  all  the 
resultant  phenomena.  In  this  way  the  science  of  Chemistry 
appears,  not  as  a  series  of  disconnected  facts,  but  as  a  harmo- 
nious and  consistent  whole. 

The  relationship  of  members  of  the  same  family  of  elements 
is  made  conspicuous,  and  resemblances  between  the  different 
families  are  pointed  out.  The  connection  between  reactions  is 
dwelt  upon,  and  where  possible  they  are  referred  to  certain  prin- 
ciples which  result  from  the  nature  of  the  component  elements. 

The  frequent  use  of  tables  and  of  comparative  summaries  lessens 
the  work  of  memorizing,  and  affords  facilities  for  rapid  reference 
to  the  usual  constants,  such  as  specific  gravity,  melting  and  boil- 
ing points,  etc.  These  tables  clearly  show  the  relationship  be- 
tween the  various  elements  and  compounds,  as  well  as  the  data 
which  are  necessary  to  emphasize  this  relationship.  They  also 
exhibit  the  structural  connection  between  existing  compounds. 

Some  descriptive  portions  of  the  work,  which  especially  refer 
to  technical  subjects,  have  been  revised  by  men  who  are  actively 
engaged  in  those  branches.  In  the  Laboratory  Appendix  will 
be  found  a  list  of  experiments,  with  descriptive  matter,  which 
materially  aid  in  the  comprehension  of  the  text. 

Professor  Walter  S.  Haines,  Rtish  Medical  College,  Chicago. :  The  work  is 
worthy  of  the  highest  praise.  The  typography  is  excellent,  the  arrange- 
ment of  the  subjects  admirable,  the  explanations  full  and  clear,  and  facts 
and  theories  are  brought  down  to  the  latest  date.  All  things  considered, 
I  regard  it  as  the  best  work  on  inorganic  chemistry  for  somewhat  advanced 
general  students  of  the  science  with  which  I  am  acquainted. 

Professor  J.  H.  Long,  Northwestern  University,  Evanston,  III.:  I  have 
looked  it  over  very  carefully,  as  at  first  sight  I  was  much  pleased  with  both 
style  and  arrangement.  Subsequent  examination  confirms  the  first  opinion 
that  we  have  here  an  excellent  and  a  very  useful  text-book.  It  is  a  book 
which  students  can  read  with  profit,  as  it  is  clear,  systematic,  and  modern. 


48  SCIENCE. 


The  Elements  of  Physics 

By  Professor  HENRY  S.  CARHART,  University  of  Michigan,  and  H.  N. 
CHUTE,  Ann  Arbor  High  School.    i2mo,  cloth,  392  pages.    Price,  $1.20. 

THIS  is  the  freshest,  clearest,  and  most  practical  manual  on 
the  subject.  Facts  have  been  presented  before  theories. 

The  experiments  are  simple,  requiring  inexpensive  apparatus, 
and  are  such  as  will  be  easily  understood  and  remembered. 

Every  experiment,  definition,  and  statement  is  the  result  of 
practical  experience  in  teaching  classes  of  various  grades. 

The  illustrations  are  numerous,  and  for  the  most  part  new, 
many  having  been  photographed  from  the  actual  apparatus  set 
up  for  the  purpose. 

Simple  problems  have  been  freely  introduced,  in  the  belief 
that  in  this  way  a  pupil  best  grasps  the  application  of  a  principle. 

The  basis  of  the  whole  book  is  the  introductory  statement 
that  physics  is  the  science  of  matter  and  energy,  and  that  noth- 
ing can  be  learned  of  the  physical  world  save  by  observation  and 
experience,  or  by  mathematical  deductions  from  data  so  obtained. 
The  authors  do  not  believe  that  immature  students  can  profitably 
be  set  to  rediscover  the  laws  of  Nature  at  the  beginning  of  their 
study  of  physics,  but  that  they  must  first  have  a  clearly  defined  idea 
of  what  they  are  doing,  an  outfit  of  principles  and  data  to  guide 
them,  and  a  good  degree  of  skill  in  conducting  an  investigation. 

William  H.  Runyon,  Armour  Institute,  Chicago :  Carhart  and  Chute's  text- 
book in  Physics  has  been  used  in  the  Scientific  Academy  of  Armour 
Institute  during  the  past  year,  and  will  be  retained  next  year.  It  has 
been  found  concise  and  scientific.  We  believe  it  to  be  the  best  book  on 
the  market  for  elementary  work  in  the  class-room. 

Professor  M.  A.  Brannon,  University  of  North  Dakota,  Grand  Forks:  I 
am  glad  to  express  the  opinion,  based  on  the  use  of  this  work  in  Elemen- 
tary Physics  last  year,  at  Fort  Wayne,  Ind.,  that  it  is  the  most  logical  and 
clear  presentation  of  the  subject  with  which  I  am  acquainted.  The  prob- 
lems associated  with  the  discussion  of  Physical  phenomena,  laws,  and  ex- 
periments serve  the  dual  purpose  of  leading  the  scholar  to  reason,  and 
put  into  practice  the  previous  clearly  and  concisely  stated  principles  of 
Elementary  Physics.  It  is  a  book  that  will  greatly  elevate  the  standard 
of  scholarship  wherever 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


MAY  9    1939 


rb    I  /U64 


